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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Nov. 06, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	ANAPTYSBIO INC
Entity Central Index Key	0001370053
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		26,751,578
Entity Emerging Growth Company	true
Transition Period	true
Entity Small Business	false

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 293,408	$ 81,189
Receivable from collaborative partners	5,000	0
Australian tax incentive receivable	173	1,601
Short-term investments	200,406	167,218
Prepaid expenses and other current assets	4,035	2,688
Total current assets	503,022	252,696
Property and equipment, net	1,344	665
Long-term investments	18,616	75,897
Other long-term assets	79	46
Restricted cash	60	60
Total assets	523,121	329,364
Current liabilities:
Accounts payable	6,180	2,323
Accrued expenses	7,145	4,875
Notes payable, current portion	7,500	6,875
Other current liabilities	48	17
Total current liabilities	20,873	14,090
Notes payable, net of current portion	2,409	7,553
Deferred rent	162	140
Stockholders’ equity:
Preferred stock, $0.001 par value, 10,000 shares authorized and no shares, issued or outstanding at September 30, 2018 and December 31, 2017, respectively	0	0
Common stock, $0.001 par value, 500,000 shares authorized, 26,749 shares and 23,791 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	27	24
Additional paid in capital	629,887	393,017
Accumulated other comprehensive loss	(541)	(426)
Accumulated deficit	(129,696)	(85,034)
Total stockholders’ equity	499,677	307,581
Total liabilities, preferred stock and stockholders’ equity	$ 523,121	$ 329,364

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	0
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	26,748,713	23,791,000
Common stock, shares outstanding (in shares)	26,748,713	23,791,000

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Collaboration revenue	$ 5,000	$ 0	$ 5,000	$ 7,000
Operating expenses:
Research and development	17,883	6,697	40,276	21,837
General and administrative	4,004	2,390	11,783	6,793
Total operating expenses	21,887	9,087	52,059	28,630
Loss from operations	(16,887)	(9,087)	(47,059)	(21,630)
Other income (expense), net:
Interest expense	(400)	(452)	(1,287)	(1,319)
Change in fair value of liability for preferred stock warrants	0	0	0	(1,366)
Interest income	1,369	358	3,851	762
Other income (expense), net	(40)	91	(167)	344
Total other income (expense), net	929	(3)	2,397	(1,579)
Net loss	(15,958)	(9,090)	(44,662)	(23,209)
Unrealized income (loss) on available for sale securities	136	16	(115)	(43)
Other comprehensive income (loss)	136	16	(115)	(43)
Comprehensive loss	$ (15,822)	$ (9,074)	$ (44,777)	$ (23,252)
Net loss per common share:
Basic and diluted (in dollars per share)	$ (0.66)	$ (0.45)	$ (1.86)	$ (1.24)
Weighted-average number of shares outstanding:
Basic and diluted (in shares)	24,146	20,382	23,961	18,668

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (44,662)	$ (23,209)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	209	136
Stock-based compensation	7,340	3,246
Change in fair value of liability for preferred stock warrants	0	1,366
(Income) loss from investments	(555)	16
Non-cash interest expense	481	460
Changes in operating assets and liabilities:
Receivable from collaborative partners	(5,000)	1,225
Australian tax incentive receivable	1,428	2,632
Prepaid expenses and other assets	(1,403)	(1,581)
Accounts payable and other liabilities	5,946	1,081
Net cash used in operating activities	(36,216)	(14,628)
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisition of investments	(123,995)	(110,701)
Sales and maturities of investments	148,551	20,866
Purchases of property and equipment	(857)	(166)
Net cash provided by (used in) investing activities	23,699	(90,001)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from public offerings, net of underwriters' fees	227,476	80,213
Proceeds from issuance of common stock, upon the exercise of stock options	2,138	814
Proceeds from issuance of common stock, upon the exercise of warrants	76	536
Payments on notes payable	(5,000)	0
Proceeds (payments) for offering costs, net	46	(1,497)
Net cash provided by financing activities	224,736	80,066
Net increase (decrease) in cash, cash equivalents, and restricted cash	212,219	(24,563)
Cash, cash equivalents and restricted cash, beginning of period	81,249	51,292
Cash, cash equivalents and restricted cash, end of period	293,468	26,729
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Interest paid	835	762
Non-cash investing and financing activities:
Amounts accrued for property and equipment	160	12
Amounts accrued for offering costs	241	215
Reclassification of warrants to equity	$ 0	$ 4,607

Description of the Business

9 Months Ended

Sep. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Description of the Business

AnaptysBio, Inc. (“we,” “us,” “our,” or the “Company”) was incorporated in the state of Delaware in November 2005. We are a biotechnology company developing first-in-class antibody product candidates focused on unmet medical needs in inflammation. We develop our product candidates using our proprietary, antibody discovery technology platform, which is designed to replicate, in vitro, the natural process of antibody generation. We currently generate revenue from milestones achieved under our collaborative research and development arrangements.

Since our inception, we have devoted our primary effort to raising capital and research and development activities. Our financial support has been provided primarily from the sale of our common and preferred stock, as well as through funds received under our collaborative research and development agreements, proceeds from our Term Loans as discussed in Note 5 below, and the issuance of convertible debt. Going forward, as we continue our expansion, we may seek additional financing and/or strategic investments. However, there can be no assurance that any additional financing or strategic investments will be available to us on acceptable terms, if at all. If events or circumstances occur such that we do not obtain additional funding, we will most likely be required to reduce our plans and/or certain discretionary spending, which could have a material adverse effect on our ability to achieve our intended business objectives. Management believes its currently available resources will provide sufficient funds to enable the Company to meet its operating plans for at least the next twelve months. The accompanying consolidated financial statements do not include any adjustments that might be necessary if we are unable to continue as a going concern.

Public Offerings and Related Transactions

Initial Public Offering

On January 31, 2017, we completed an initial public offering, or IPO, selling 5,750,000 shares of common stock at $15.00 per share. Proceeds from our initial public offering net of underwriting discounts and commissions were $80.2 million.

In addition, each of the following occurred in connection with the completion of the IPO on January 31, 2017:


•	the conversion of all outstanding shares of convertible preferred stock into 11,520,698 shares of common stock; and


•	the conversion of warrants to purchase 377,195 shares of convertible preferred stock into warrants to purchase 377,195 shares of common stock and the resultant reclassification of the warrant liability to additional paid-in capital.

Reverse Stock Split

On January 13, 2017, we amended and restated our certificate of incorporation to effect a one for seven reverse stock split of every outstanding share of our preferred and common stock. The financial statements and accompanying footnotes have been retroactively restated to reflect the reverse stock split.

Follow-on Public Offerings

On October 17, 2017, we completed an underwritten public offering selling 3,000,000 shares of common stock. All shares were offered by us at a price to the public of $68.50 per share. The aggregate net proceeds received by us from the offering were $194.7 million, net of underwriting discounts and commissions. As part of the underwritten public offering, on November 14, 2017, the underwriters exercised an additional 271,380 shares of common stock at a discounted price to the public of $68.50 per share for aggregate net proceeds of $17.6 million, net of underwriting discounts and commissions.

On September 28, 2018, we completed an underwritten public offering of 2,530,000 shares of common stock, which included the exercise of the underwriters’ option to purchase an additional 330,000 shares of common stock. All shares were offered by us at a price to the public of $94.46 per share. The aggregate net proceeds received by us from the offering were $227.5 million, net of underwriting discounts and commissions.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission, or the SEC. Certain information and note disclosures normally included in annual financial statements prepared in accordance with U.S. generally accepted accounting principles, or U.S. GAAP, have been omitted. The accompanying unaudited consolidated financial statements include all known adjustments necessary for a fair presentation of the results of interim periods as required by U.S. GAAP. These adjustments consist primarily of normal recurring accruals and estimates that impact the carrying value of assets and liabilities. Operating results for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018. The financial statements should be read in conjunction with our audited financial statements for the year ended December 31, 2017, included in our Annual Form 10-K, as amended on September 14, 2018.

Basis of Consolidation

The accompanying consolidated financial statements include us and our wholly-owned Australian subsidiary. All intercompany accounts and transactions have been eliminated in consolidation. We operate in one reportable segment and our functional and reporting currency is the U.S. dollar.

Use of Estimates

The preparation of the accompanying consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. We base our estimates and assumptions on historical experience when available and on various factors that we believe to be reasonable under the circumstances. We evaluate our estimates and assumptions on an ongoing basis. Our actual results could differ from these estimates under different assumptions or conditions.

Revenue Recognition

Revenue is recognized in accordance with revenue recognition accounting guidance, which utilizes five basic steps to determine whether revenue can be recognized and to what extent: (i) identify the contract with a customer; (ii) identify the performance obligation; (iii) determine the transaction price; (iv) allocate the transaction price; and (v) determine the recognition period.

Performance Obligations. We evaluate deliverables on a contract by contract basis to determine whether each deliverable represents a good or service that is distinct or has the same pattern of transfer as other deliverables. A deliverable is considered distinct if the customer can benefit from the good or service independently of other goods/services either in the contract or that can be obtained elsewhere, without regard to contract exclusivity, and the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contact. If the deliverable is not considered distinct, we combine such deliverables and account for them as a single performance obligation. We allocate the consideration to each deliverable at the inception of the arrangement based on the transaction price.

Our performance obligations may include the following:

•

License Arrangements. The performance obligations under our collaboration and license agreements generally include exclusive or nonexclusive licenses to one or more products generated using our technologies. Licenses for multiple antibodies within a single contract are generally combined as they have substantially the same pattern of transfer to the customer. Historically, our licenses have held no value to the customer, as the antibodies were in the discovery phase and required our expertise for further development. Accordingly, licenses are not considered distinct.

•

Research and Development Services. The performance obligations under our collaboration and license agreements generally include research and development services we perform on behalf of or with our collaborators. As discussed within license arrangements above, our licenses have historically held no value without the research and development services we provide. As we generally only provide research and development services for internally generated antibodies that require a license to be utilized by a third party, our research and development services are not considered distinct.


•	Steering Committee Meetings. The performance obligations under our collaboration and license agreements may also include our participation in a steering committees, which allows us to direct the progression of our discovery programs. As these steering committees would not occur or benefit the customer without the use of our licenses, these are not considered distinct.

We recognize consideration allocated to a performance obligation as the performance obligation is satisfied, and the determination as to whether consideration is recognized over time or at a point in time is made upon contract inception. For our collaboration agreements, this is generally over the period in which research and development services have been performed.

Transaction Price. Our collaboration and license agreements generally include both fixed and variable consideration. Fixed payments, such as those for upfront fees are included in the transaction price at contract value, while variable consideration such as reimbursement for research and development services, milestone and royalty payments are estimated and then evaluated for constraints upon inception of the contract and evaluated on a quarterly basis thereafter. Research and development services are updated for actual invoices. Given the nature of our agreements, milestones are estimated using the most likely amount and are evaluated on a quarterly basis. Upon commercialization, royalty payments are recognized in the period incurred.

Net Loss Per Common Share

Basic net loss per common share is computed by dividing net loss by the weighted-average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing net loss by the weighted-average number of common equivalent shares outstanding for the period. Diluted net loss per share includes any dilutive effect from outstanding stock options and warrants using the treasury stock method. For each period presented, there is no difference in the number of shares used to calculate basic and diluted net loss per share.

The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in common stock equivalent shares):



	Three Months Ended September 30,		Nine Months Ended September 30,
(in thousands)	2018	2017	2018	2017
Options to purchase common stock	2,402	1,755	2,514	1,883
Warrants to purchase common stock	—	—	3	209
Total	2,402	1,755	2,517	2,092

Accounting Pronouncements Recently Adopted

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers, which outlines a single comprehensive model for entities to use in accounting for revenue from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. This standard is based on the principle that an entity should recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This standard also requires additional disclosure about the nature, amount, timing and uncertainty of assets recognized from costs incurred to fulfill a contract and became effective for our annual reporting period beginning January 1, 2018, including interim periods within that reporting period. Entities have the option of using either a full retrospective or a modified retrospective approach for the adoption of the new standard. We assessed all potential impacts of the standard, and the most significant impacts relate to our accounting for variable consideration including revenues related to contingent “milestone” based payments and our disclosures required under the new standard as it relates to our two ongoing collaboration agreements, TESARO and Celgene. Application of the new standard requires that variable consideration be recognized to the extent that it is probable that a significant reversal in the amount of revenue will not occur when the uncertainty associated with the variable consideration is subsequently resolved. Accordingly, we may be required to recognize milestone payments earlier in the period in which we determine a significant reversal will not occur, rather than when the milestone is achieved. However, we have reviewed the TESARO and Celgene agreements and have determined that given the nature of potential milestones owed to us under these agreements, and the inherent risk involved in developing drugs, and have determined that these potential milestones were not recognizable as of the standard adoption date. Additionally, while we currently disaggregate our revenue disclosures by collaborative agreement, additional discussion surrounding significant estimates made by management was required in our disclosure and included in Note 4 below. We adopted this standard using the modified retrospective approach for our annual reporting period beginning January 1, 2018, and did not record any adjustments upon adoption of this standard.

In January 2016, the FASB issued ASU 2016-01, Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, which intends to enhance the reporting model for financial instruments by providing users of financial instruments with more decision-useful information. The standard also addresses certain aspects of the recognition, measurement, presentation, and disclosure of financial instruments and requires additional disclosure about the nature, amount, timing and uncertainty of assets recognized from costs incurred to fulfill a contract and became effective for our annual reporting period beginning January 1, 2018, including interim periods within that reporting period; early adoption is permitted. We adopted this standard as of January 1, 2018 and there was no material impact on our consolidated financial statements. We did not record any adjustments upon adoption of this standard and have consistently applied our accounting policies to all periods presented in the consolidated financial statements.

In May 2017, the FASB issued ASU 2017-09, Compensation - Stock Compensation (Topic 718), which provides further guidance as to what constitutes a modification to the terms of shared based compensation, in order to create consistency in practice amongst all entities. ASU 2017-09 became effective for annual reporting periods beginning after December 15, 2017, including interim periods thereafter; early adoption is permitted, including adoption in an interim period. We adopted this standard as of January 1, 2018, and the impact was not material on our consolidated financial statements. We did not record any adjustments upon adoption of this standard.

Recent Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires that lessees recognize a right-of-use, or “ROU”, asset and a related lease liability on the balance sheet for all leases with a term longer than 12 months. Topic 842 was subsequently amended by ASU 2018-01, Land Easement Practical Expedient for Transition to Topic 842; ASU 2018-10, Codification Improvements to Topic 842, Leases; and ASU 2018-11, Targeted Improvements. ASU 2016-02 becomes effective for our annual reporting period beginning January 1, 2019, including interim periods thereafter; early adoption is permitted. A modified retrospective transition approach is required, applying the new standard to all leases existing at the date of initial application. An entity may choose to use either (i) its effective date or (ii) the beginning of the earliest comparative period presented in the financial statements as its date of initial application. We expect to adopt the new standard on January 1, 2019 and use the effective date as our date of initial application. The new standard provides a number of optional practical expedients in transition. We expect to elect the ‘package of practical expedients’, which permits us not to reassess under the new standard our prior conclusions about lease identification, lease classification and initial direct costs. While we continue to assess all of the effects of adoption, we expect the recognition of new ROU assets and lease liabilities on our balance sheet for current real estate leases as well as the enhanced disclosure requirements will not have a material effect on our financial statements.

Balance Sheet Accounts and Supplemental Disclosures

9 Months Ended

Sep. 30, 2018

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Accounts and Supplemental Disclosures

Property and Equipment

Property and equipment consist of the following:



(in thousands)	September 30, 2018			December 31, 2017
Laboratory equipment	$	4,138		$	3,687
Office furniture and equipment	723			605
Leasehold improvements	575			351
Property and equipment, gross	$	5,436		$	4,643
Less: accumulated depreciation and amortization	(4,092		)	(3,978		)
Total property and equipment, net	$	1,344		$	665

Accrued Expenses

Accrued expenses consist of the following:



(in thousands)	September 30, 2018		December 31, 2017
Accrued compensation and related expenses	$	2,176	$	1,588
Accrued research and contract manufacturing expenses	4,196		2,961
Other	773		326
Total accrued expenses	$	7,145	$	4,875

Collaborative Research and Development Agreements

9 Months Ended

Sep. 30, 2018

Revenue Recognition [Abstract]

Collaborative Research and Development Agreements

TESARO Collaboration

In March 2014, we entered into a Collaboration and Exclusive License Agreement, or the TESARO Agreement, with TESARO, Inc. and TESARO Development, Inc., or collectively, TESARO, an oncology-focused biopharmaceutical company. Under the terms of the agreement, we agreed to perform certain discovery and early preclinical development of therapeutic antibodies with the goal of generating immunotherapy antibodies for subsequent preclinical, clinical, regulatory and commercial development to be performed by TESARO. Under the terms of the agreement, TESARO paid an upfront license fee of $17.0 million in March 2014 and agreed to provide funding to us for research and development services related to antibody discovery programs for three specific targets. In November 2014, we and TESARO entered into Amendment No. 1 to the Agreement to add an antibody discovery program against an undisclosed fourth target for an upfront license fee of $2.0 million.

For each development program, we are eligible to receive milestone payments of up to $18.0 million if certain preclinical and clinical trial events are achieved by TESARO, up to an additional $90.0 million if certain U.S. and European regulatory submissions and approvals in multiple indications are achieved, and up to an additional $165.0 million upon the achievement of specified levels of annual worldwide net sales. We will also be eligible to receive tiered single-digit royalties related to worldwide net sales of products developed under the collaboration. Unless earlier terminated by either party upon specified circumstances, the agreement will terminate, with respect to each specific developed product, upon the latter of the 12th anniversary of the first commercial sale of the product or the expiration of the last to expire of any patent. Prior to the adoption of ASC Topic 606, we determined that the upfront license fees and research funding under the agreement, as amended, should be accounted for as a single unit of accounting and that the upfront license fees should be deferred and recognized as revenue over the same period that the research and development services are performed. In December 2015, we determined that the research and development services would be extended through December 31, 2016. As a result, the period over which the unrecognized license fees and milestones were recognized was extended through December 31, 2016, and have been recognized in full.

We assessed this arrangement in accordance with ASC Topic 606 and concluded that the contract counterparty, TESARO, is a customer. We identified the following material promises under the TESARO Agreement: (1) the licenses under certain patent rights relating to six discovery programs (four targets) and transfer of certain development and regulatory information, (2) R&D services and (3) Joint Steering Committee meetings. We considered the research and discovery capabilities of TESARO for these specific programs, TESARO’s inability to sub-license, and the fact that the discovery and optimization of these antibodies is proprietary and could not, at the time of the contract inception, be provided by other vendors, to conclude that the license does not have stand-alone functionality and is therefore not distinct. Additionally, we determined that the steering committee participation would not have been provided without the R&D services and license agreement. Based on these assessments, we identified all services to be interrelated, and therefore concluded that the promises should be combined into a single performance obligation at the inception of the arrangement.

As of September 30, 2018, the transaction price includes the upfront payment, research reimbursement revenue, and milestones earned to date, which are allocated in their entirety to the single performance obligation. We recognized one future clinical milestone for $5.0 million during the three months ended September 30, 2018 upon determination that a significant reversal of revenue would not be probable. No other future clinical or regulatory milestones have been included in the transaction price, as all milestone amounts were subject to the revenue constraint. As part of the constraint evaluation, we considered numerous factors including the fact that the receipt of milestones is outside of our control and contingent upon success in future clinical trials, an outcome that is difficult to predict, and the licensees’ efforts. Any consideration related to sales-based milestones, including royalties, will be recognized when the related sales occur as they were determined to relate predominantly to the IP license granted to TESARO and therefore have also been excluded from the transaction price. We will re-evaluate the variable transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur.

Milestones recognized through September 30, 2018 under the TESARO Agreement are as follows:



	Anti-PD-1 (TSR042)		Anti-TIM-3 (TSR022)		Anti-LAG-3 (TSR033)
Milestone Event	Amount	Quarter Recognized	Amount	Quarter Recognized	Amount	Quarter Recognized
Initiated in vivo toxicology studies using good laboratory practices (GLPs)	$1.0M	Q2'15	$1.0M	Q4'15	$1.0M	Q3'16
IND clearance from the FDA	$4.0M	Q1'16	$4.0M	Q2'16	$4.0M	Q2'17
Phase 2 clinical trial initiation	$3.0M	Q2'17	$3.0M	Q4'17	—	—
Phase 3 clinical trial initiation	$5.0M	Q3'18	—	—	—	—

Milestones achieved during the discovery period were recognized as revenue pro-rata through December 31, 2016. Milestones achieved during fiscal 2017 were recognized as revenue in the period earned, while milestones after December 31, 2017 were recognized upon determination that a significant reversal of revenue would not be probable. Cash is generally received within 30 days of milestone achievement.

Revenue from future contingent milestone payments will be recognized when it is more likely than not that the revenue will not be reversed in future periods.

We recognized $5.0 million in revenue under this agreement during the three and nine months ended September 30, 2018 related to one milestone upon determination that a significant reversal of revenue would not be probable, and $7.0 million in revenue under this agreement during the nine months ended September 30, 2017 related to two milestones. There was no revenue recognized under this agreement during the three months ended September 30, 2017.

Antibody Generation Agreement with Celgene Corporation

In December 2011, we entered into a license and collaboration agreement with Celgene, or the Celgene Agreement, to develop therapeutic antibodies against multiple targets. We granted Celgene the option to obtain worldwide commercial rights to antibodies generated against each of the targets under the agreement, which option was triggered on a target-by-target basis by our delivery of antibodies meeting certain pre-specified parameters pertaining to each target under the agreement.

The agreement provided for an upfront payment of $6.0 million from Celgene, which we received in 2011 and recognized through 2014, milestone payments of up to $53.0 million per target, low single-digit royalties on net sales of antibodies against each target, and reimbursement of specified research and development costs.

We assessed this arrangement in accordance with ASC Topic 606 and concluded that the contract counterparty, Celgene, is a customer. We identified the following material promises under the Celgene Agreement: (1) the licenses under certain patent rights relating to four targets and transfer of certain development and regulatory information, (2) R&D services, (3) a written report documenting findings and (4) Steering Committee meetings. We considered the research and discovery capabilities of Celgene, Celgene’s inability to sub-license the four targets, and the fact that the discovery and optimization of these antibodies is proprietary and could not, at the time of the contract inception, be provided by other vendors, to conclude that the license does not have stand-alone functionality and is therefore not distinct. Additionally, we determined that the report of findings and steering committee participation would not have been provided without the R&D services and license agreement. Based on these assessments, we identified all services to be interrelated, and therefore concluded that the promises should be combined into a single performance obligation at the inception the arrangement.

As of September 30, 2018, the transaction price includes the upfront payment, success fees, expense reimbursement, and milestones earned to date, which are allocated in their entirety to the single performance obligation. None of the future clinical or regulatory milestones have been included in the transaction price, as all milestone amounts were subject to the revenue constraint. As part of the constraint evaluation, we considered numerous factors, including the fact that the receipt of milestones is outside of our control and contingent upon success in future clinical trials and the licensees’ efforts. Any consideration related to sales-based milestones, including royalties, will be recognized when the related sales occur as they were determined to relate predominantly to the IP license granted to Celgene and therefore have also been excluded from the transaction price. We will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur.

Milestones achieved through September 30, 2018 under the Celgene Agreement are as follows:



	Anti-PD-1 (CC-90006)
Milestone Event	Amount	Quarter Recognized
Completion of first in vivo toxicology studies using GLPs	$0.5M	Q2'16
Phase 1 clinical trial initiation	$1.0M	Q4'16

Revenue from future contingent milestone payments will be recognized when it is more likely than not that the revenue will not be reversed in future periods. Cash is generally received within 30 days of milestone achievement.

There was no revenue recognized under this agreement during the three and nine months ended September 30, 2018 and 2017.

Notes Payable	9 Months Ended
Notes Payable	Sep. 30, 2018
Debt Disclosure [Abstract]
Notes Payable	Notes Payable On December 24, 2014, we entered into a Loan and Security Agreement, as amended from time to time, the Loan Agreement, with a bank and a financial institution whereby we may borrow up to $15.0 million in three separate draws of $5.0 million each. The Term A Loans, for an aggregate of $5.0 million, were drawn on December 24, 2014 with a fixed interest rate of 6.97%. In connection with the issuance of the Term A Loans, we issued detachable, fully vested warrants to purchase an aggregate of 41,208 shares of Series C Preferred Stock at an exercise price of $4.55 per share to the lenders. The grant-date fair value of the warrants of $0.1 million was recorded as a liability, with a reduction to the carrying value of the Term A Loans, and which is recognized as additional interest expense over the remaining term of the Loans. The initial fair value of the warrants was determined using the Black-Scholes option pricing model with the following assumptions: a stock price volatility of 70.2%, an expected life equal to the contractual term of the warrants of ten years and a risk-free interest rate of 1.97%. In January 2016, the Loan Agreement was amended to combine Term B Loans and Term C Loans for a total of $10.0 million available for draw through December 31, 2016 and delay the beginning of our Term A Loans’ principal repayments from February 1, 2016 until February 1, 2017. The Term B Loans and Term C Loans became available for draw on July 1, 2016. In December 2016, we further amended the Loan Agreement to (i) allow for the Term B Loans and Term C Loans to be drawn on December 30, 2016, (ii) delay principal repayments of all Term Loans until February 1, 2018 and (iii) amend the interest rate for each Term Loan. The Term B Loans and the Term C Loans were drawn on December 30, 2016, and Term A, B and C Loans are now collectively referred to as the Term Loans. Principal repayments began in February 2018, and as of September 30, 2018, there are 16 monthly principal and interest payments remaining on the Term Loans, with final maturity in January 2020. The Term Loans bear interest equal to the greater of 3-month U.S. LIBOR plus 6.37% or 7.3%. The interest rate was 8.69% as of September 30, 2018. In connection with the issuance of the Term B & C Loans, we issued detachable, fully vested warrants to purchase an aggregate of 82,416 shares of Series C Preferred Stock at an exercise price of $4.55 per share to the lenders. The grant-date fair value of the warrants of $0.9 million was recorded as a liability, with a reduction to the carrying value of the Term B & C Loans, and which is recognized as additional interest expense over the remaining term of the Loans. The initial fair value of the warrants was determined using the Black-Scholes option pricing model with the following assumptions: a stock price volatility of 79.2%, an expected life equal to the contractual term of the warrants of ten years and a risk-free interest rate of 2.45%. As discussed in Note 1 above, all of the outstanding warrants to purchase shares of preferred stock automatically converted into warrants to purchase shares of common stock in connection with the IPO and were accounted for as equity from the conversion date forward. All warrants related to Term Loans were exercised during the year ended December 31, 2017. The costs incurred to issue the Term Loans were deferred and are included in the discount to the carrying value of the Term Loans in the accompanying balance sheet. The Term Loans also include a final payment fee of $0.8 million due at the earlier of prepayment or the maturity date of the Term Loans. The deferred costs and the final payment fee are being amortized to interest expense over the expected term of the Term A Loans using the effective interest method. As of September 30, 2018, the carrying amount of the Term Loans was $9.9 million, which is net of unamortized discounts of $0.1 million and of which $7.5 million is classified as current liabilities as of September 30, 2018. The effective interest rate on the Term Loans at September 30, 2018 was 13.08%. As of September 30, 2018, future principal maturities of the Term Loans were $1.9 million, $7.5 million and $0.6 million in 2018, 2019 and 2020, respectively. The Term Loans are secured by a first priority interest in most of our assets, excluding intellectual property. As of September 30, 2018, we were in compliance with the covenants contained in the Loan Agreement.

Fair Value Measurements and Available for Sale Investments

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements and Available for Sale Investments

Fair Value Measurements

Our financial instruments consist principally of cash, cash equivalents, restricted cash, short-term and long-term investments, receivables, accounts payable, notes payable and, through January 31, 2017, preferred stock warrant liabilities. Certain of our financial assets and liabilities have been recorded at fair value in the consolidated balance sheet in accordance with the accounting standards for fair value measurements.

Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. Accounting guidance also establishes a fair value hierarchy that requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The standard describes three levels of inputs that may be used to measure fair value:

Level 1 - Observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets.

Level 2 - Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and

Level 3 - Unobservable inputs that are supported by little or no market activities, therefore requiring an entity to develop its own assumptions.

Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following table summarizes our assets and liabilities that require fair value measurements on a recurring basis and their respective input levels based on the fair value hierarchy:



	Fair Value Measurements at End of Period Using:
(in thousands)	Fair Value		Quoted Market Prices for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
At September 30, 2018
Money market funds⁽¹⁾	$	51,442	$	51,442	$	—	$	—
Mutual funds⁽¹⁾	236,332		236,332		—		—
U.S. treasury securities⁽²⁾	95,086		95,086		—		—
Certificates of deposit⁽²⁾	959		—		959		—
Agency securities⁽²⁾	44,647		—		44,647		—
Commercial and corporate obligations⁽¹⁾⁽²⁾	80,646		—		80,646		—
At December 31, 2017
Money market funds⁽¹⁾	$	41,318	$	41,318	$	—	$	—
Mutual funds⁽¹⁾	28,817		28,817		—		—
U.S. treasury securities⁽²⁾	79,397		79,397		—		—
Agency securities⁽²⁾	59,948		—		59,948		—
Commercial and corporate obligations⁽²⁾	111,660		—		111,660		—


⁽¹⁾	Included in cash and cash equivalents, and restricted cash in the accompanying consolidated balance sheets.


⁽²⁾	Included in short-term or long-term investments in the accompanying consolidated balance sheets depending on the respective maturity date.

The following methods and assumptions were used to estimate the fair value of our financial instruments for which it is practicable to estimate that value:

Marketable Securities. For fair values determined by Level 1 inputs, which utilize quoted prices in active markets for identical assets, the level of judgment required to estimate fair value is relatively low. For fair values determined by Level 2 inputs, which utilize quoted prices in less active markets for similar assets, the level of judgment required to estimate fair value is also considered relatively low.

Warrant Liabilities. Our preferred stock warrants were accounted for as derivative liabilities and measured at fair value on a recurring basis through January 31, 2017 as they contained features that were either not afforded equity classification or embodied risks that were not clearly and closely related to host contracts. We estimated the fair value of these derivatives utilizing the Black-Scholes option-pricing model, which required Level 3 inputs.

As discussed in Note 1 above, all of the outstanding warrants to purchase shares of preferred stock automatically converted into warrants to purchase shares of common stock in connection with the IPO and are accounted for as equity from the conversion date forward. Prior to the conversion, we estimated the fair value of convertible preferred stock warrants at the time of issuance and upon subsequent remeasurement using the Black-Scholes option-pricing model at each reporting date.

Estimating fair values of derivative financial instruments, including Level 3 instruments, requires the use of significant and subjective inputs that may, and are likely to, change over the duration of the instrument with related changes in internal and external market factors, including changes in the estimated fair value of our equity securities.

The following weighted-average assumptions were utilized in estimating the value of the liabilities for Series C preferred stock warrants using the Black-Scholes option-pricing model as of January 31, 2017, the conversion date:



	January 31, 2017
Fair value of preferred stock	$	16.95
Exercise price	$	4.55
Risk-free interest rate	1.4		%
Volatility	88.8		%
Dividend Yield	—		%
Contractual term (in years)	3.8
Weighted-average measurement date fair value per share	$	13.71

The following table summarizes the activity in liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3 Inputs):



	Nine Months Ended September 30,
(in thousands)	2017
Preferred Stock Warrant Liabilities:
Beginning balance	$	(3,241	)
Net gains (losses) included in other expense	(1,366		)
Reclassification of warrant liabilities to equity	4,607
Ending balance	$	—

Fair Value of Other Financial Instruments

The fair value of our other financial instruments estimated as of September 30, 2018 and December 31, 2017 are presented below:



	September 30, 2018				December 31, 2017
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Notes payable	$	9,909	$	10,671	$	14,428	$	15,650

The following methods and assumptions were used to estimate the fair value of our notes payable:

Notes Payable—We use the income approach to value the aforementioned debt instrument. We use a present value calculation to discount principal and interest payments and the final maturity payment on these liabilities using a discounted cash flow model based on observable inputs. We discount these debt instruments based on what the current market rates would offer us as of the reporting date. Based on the assumptions used to value these liabilities at fair value, these debt instruments are categorized as Level 2 in the fair value hierarchy.

The carrying amounts of certain of our financial instruments, including cash and cash equivalents, Australian tax incentive receivable, accounts payable, and accrued expenses approximate fair value due to their short-term nature.

Available for Sale Investments

We invest our excess cash in agency securities, debt instruments of financial institutions and corporations, commercial obligations, and U.S. Treasury securities, which we classify as available-for-sale investments. These investments are carried at fair value and are included in the tables above. The aggregate market value, cost basis, and gross unrealized gains and losses of available-for-sale investments by security type, classified in cash equivalents, short-term and long-term investments as of September 30, 2018 are as follows:



(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Total Fair Value
Agency securities⁽¹⁾	$	44,832	$	—	$	(185	)	$	44,647
Certificates of deposit⁽²⁾	959		—		—			959
Commercial and corporate obligations⁽³⁾	80,812		1		(167		)	80,646
US Treasury securities⁽⁴⁾	95,276		—		(190		)	95,086
Total available-for-sale investments	$	221,879	$	1	$	(542	)	$	221,338


⁽¹⁾	Of our outstanding agency securities, $42.9 million have maturity dates of less than one year and $1.7 million have a maturity date of between one to two years as of September 30, 2018.


⁽²⁾	All of our outstanding certificates of deposit have a maturity date of between one to two years as of September 30, 2018.


⁽³⁾	Of our outstanding commercial and corporate obligations, $74.6 million have maturity dates of less than one year and $6.1 million have a maturity date of between one to two years as of September 30, 2018.


⁽⁴⁾	Of our outstanding U.S. Treasury securities $85.2 million have maturity dates of less than one year and $9.9 million have a maturity date of between one to two years as of September 30, 2018.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Stockholders' Equity

9 Months Ended

Sep. 30, 2018

Equity [Abstract]

Stockholders' Equity

Stockholders’ Equity

Common and Preferred Stock

On January 31, 2017, upon completion of our IPO, we amended our Certificate of Incorporation to increase the number of authorized shares of common stock to 500,000,000 with a par value of $0.001 and decrease the number of authorized shares of preferred stock to 10,000,000 with a par value of $0.001 per share.

Common Stock

Of the 500,000,000 shares of common stock authorized, 26,748,713 shares were issued and outstanding as of September 30, 2018. Common stock reserved for future issuance upon the exercise, issuance or conversion of the respective equity instruments at September 30, 2018 are as follows:



Issued and Outstanding:
Stock options	2,308,389
Shares Reserved For:
2017 Equity Incentive Plan	2,038,194
Employee Stock Purchase Plan	455,913
Total	4,802,496

Warrant Exercises

During the nine months ended September 30, 2018, 16,770 shares of common stock were issued as a result of warrant exercises. During the nine months ended September 30, 2017, warrants for the purchase of 476,251 shares of common stock were exercised, of which 358,342 were exercised by a net exercise method. As a result, we issued 397,445 shares of common stock, net. As of September 30, 2018, all warrants have been exercised.

Equity Incentive Plans

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Equity Incentive Plans

2017 Equity Incentive Plan

On January 12, 2017, our board of directors and stockholders approved and adopted the 2017 Equity Incentive Plan, or the 2017 Plan. The 2017 Plan became effective upon the execution and delivery of the underwriting agreement for our initial public offering on January 26, 2017, and replaced our existing 2006 Equity Incentive Plan, or the 2006 Plan. Under the 2017 Plan we may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other awards to individuals who are then our employees, officers, directors or consultants. In addition, the number of shares of stock available for issuance under the 2017 Plan will be automatically increased each January 1, beginning on January 1, 2018, by 4% of the aggregate number of outstanding shares of our common stock as of the immediately preceding December 31 or such lesser number as determined by our board of directors. The 2017 Plan automatically increased by 951,656 shares as of January 1, 2018.

Employee Stock Purchase Plan

On January 12, 2017, our board of directors and stockholders approved and adopted the 2017 Employee Stock Purchase Plan or the ESPP. The ESPP became effective upon the execution and delivery of the underwriting agreement for our initial public offering on January 26, 2017. In addition, the number shares of stock available for issuance under the ESPP will be automatically increased each January 1, beginning on January 1, 2018, by 1% of the aggregate number of outstanding shares of our common stock as of the immediately preceding December 31 or such lesser number as determined by our board of directors. The ESPP automatically increased by 237,913 shares as of January 1, 2018.

Stock Options

Stock options granted to employees and non-employees generally vest over a four-year period while stock options granted to directors vest over a one year period. Additionally, new non-employee directors receive stock options that vest over a three-year period. Each have a maximum term of ten years from the date of grant, subject to earlier cancellation prior to vesting upon cessation of service to us. A summary of the activity related to stock option awards during the nine months ended September 30, 2018 is as follows:



	Shares Subject to Options		Weighted-Average Exercise Price per Share		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at January 1, 2018	2,425,903		$	12.03
Granted	339,557		$	100.98
Exercises	(410,551	)	$	5.21
Forfeitures and cancellations	(46,520	)	$	49.68
Outstanding at September 30, 2018	2,308,389		$	25.57	7.25	$	173,085
Exercisable at September 30, 2018	1,330,540		$	10.62	6.27	$	118,779

Total cash received from the exercise of stock options was approximately $2.1 million during the nine months ended September 30, 2018.

Certain stock option grants under the 2006 Plan provide for exercise of the stock option prior to vesting. Shares of common stock issued upon exercise of unvested options are subject to repurchase by us at the respective original exercise price until vested. Consideration received for the exercise of unvested stock options is recorded as a liability and reclassified into equity as the related award vests.

Stock-Based Compensation Expense

The estimated fair values of stock option awards granted to employees were determined on the date of grant using the Black-Scholes option valuation model with the following weighted average assumptions:



	Nine Months Ended September 30,
	2018			2017
Risk-free interest rate	2.6		%	2.0		%
Expected volatility	68.0		%	64.4		%
Expected dividend yield	—		%	—		%
Expected term (in years)	6.25			6.25
Weighted average grant date fair value per share	$	63.49		$	22.54

We determine the appropriate risk free interest rate, expected term for employee stock based awards, contractual term for non-employee stock based awards, and volatility assumptions. The weighted-average expected option term for employee and director stock based awards reflects the application of the simplified method, which defines the life as the average of the contractual term of the options and the weighted average vesting period for all option tranches. The weighted average expected term for non-employee stock based awards is the remaining contractual life of the award. Estimated volatility incorporates historical volatility of our common stock and similar entities whose share prices are publicly available. The risk free interest rate is based upon U.S. Treasury securities with remaining terms similar to the expected or contractual term of the share based payment awards. The assumed dividend yield is based on our expectation of not paying dividends in the foreseeable future.

There were 339,557 and 1,061,106 stock options granted during the nine months ended September 30, 2018 and 2017, respectively.

Total non-cash stock-based compensation expense for all stock awards that was recognized in the consolidated statements of operations and comprehensive loss is as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2018		2017		2018		2017
Research and development	$	837	$	198	$	2,492	$	997
General and administrative	1,695		744		4,848		2,249
Total	$	2,532	$	942	$	7,340	$	3,246

At September 30, 2018, there was $27.8 million of unrecognized compensation cost related to unvested stock option awards, which is expected to be recognized over a remaining weighted average vesting period of 2.46 years.

Australia Research and Development Tax Incentive	9 Months Ended
Australia Research and Development Tax Incentive	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Australia Research and Development Tax Incentive	Australia Research and Development Tax Incentive Our Australian subsidiary, which conducts core research and development activities on our behalf, is eligible to receive a 43.5% refundable tax incentive for qualified research and development activities during fiscal 2018 and fiscal 2017. For the three months ended September 30, 2018 and 2017, less than $0.1 million and $0.2 million, respectively, were recorded as a reduction to research and development expenses in the consolidated statements of operations and comprehensive loss. For the nine months ended September 30, 2018 and 2017 $0.1 million and $1.4 million, respectively, were recorded as a reduction to research and development expenses in the consolidated statements of operations and comprehensive loss. As of September 30, 2018 our tax incentive receivable from the Australian government was $0.2 million. We received approximately $1.5 million and $4.6 million in cash during the nine months ended September 30, 2018 and 2017, respectively, related to the tax incentive.

Commitments and Contingencies

9 Months Ended

Sep. 30, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Operating Leases

In May 2018, we entered into a three year sub-lease agreement for an additional 18,000 square feet of office space. We also continue to lease our headquarters under a non-cancellable operating lease for which we early exercised our option to renew for an additional five-year period in fiscal 2015. Both leases expire in 2021.

At September 30, 2018, the future minimum annual obligations under non-cancellable operating lease commitments are as follows:



Years Ending December 31, (in thousands)
2018	$	201
2019	938
2020	968
2021	726
2022	—
Thereafter	—
Total minimum payments required	$	2,833

Other Commitments and Contingencies

We have entered into agreements with certain vendors for the provision of goods and services, which includes manufacturing services with contract manufacturing organizations and development services with contract research organizations. These agreements may include certain provisions for purchase obligations and termination obligations that could require payments for the cancellation of committed purchase obligations or for early termination of the agreements. The amount of the cancellation or termination payments vary and are based on the timing of the cancellation or termination and the specific terms of the agreement.

We also have certain obligations under licensing agreements with third parties that are contingent upon achieving various development, regulatory and commercial milestones. Pursuant to these license agreements, we are required to make milestone payments if certain development, regulatory and commercial sales milestones are achieved. Also, pursuant to the terms of each of these license agreements, when and if commercial sales of a product commence, we will pay royalties to our licensors on net sales of the respective products.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Basis of Presentation

Basis of Consolidation

Use of Estimates

Revenue Recognition

Our performance obligations may include the following:

•


•	Steering Committee Meetings. The performance obligations under our collaboration and license agreements may also include our participation in a steering committees, which allows us to direct the progression of our discovery programs. As these steering committees would not occur or benefit the customer without the use of our licenses, these are not considered distinct.

Net Loss Per Common Share

Accounting Pronouncements Recently Adopted and Recent Accounting Pronouncements

Accounting Pronouncements Recently Adopted

Recent Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Schedule of Outstanding Potentially Dilutive Securities Excluded in the Calculation of Diluted Net Loss Per Share



	Three Months Ended September 30,		Nine Months Ended September 30,
(in thousands)	2018	2017	2018	2017
Options to purchase common stock	2,402	1,755	2,514	1,883
Warrants to purchase common stock	—	—	3	209
Total	2,402	1,755	2,517	2,092

Balance Sheet Accounts and Supplemental Disclosures (Tables)

9 Months Ended

Sep. 30, 2018

Balance Sheet Related Disclosures [Abstract]

Property and Equipment

Property and equipment consist of the following:



(in thousands)	September 30, 2018			December 31, 2017
Laboratory equipment	$	4,138		$	3,687
Office furniture and equipment	723			605
Leasehold improvements	575			351
Property and equipment, gross	$	5,436		$	4,643
Less: accumulated depreciation and amortization	(4,092		)	(3,978		)
Total property and equipment, net	$	1,344		$	665

Schedule of Accrued Expenses

Accrued expenses consist of the following:



(in thousands)	September 30, 2018		December 31, 2017
Accrued compensation and related expenses	$	2,176	$	1,588
Accrued research and contract manufacturing expenses	4,196		2,961
Other	773		326
Total accrued expenses	$	7,145	$	4,875

Collaborative Research and Development Agreements (Tables)

9 Months Ended

Sep. 30, 2018

Revenue Recognition [Abstract]

Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions

Milestones recognized through September 30, 2018 under the TESARO Agreement are as follows:



	Anti-PD-1 (TSR042)		Anti-TIM-3 (TSR022)		Anti-LAG-3 (TSR033)
Milestone Event	Amount	Quarter Recognized	Amount	Quarter Recognized	Amount	Quarter Recognized
Initiated in vivo toxicology studies using good laboratory practices (GLPs)	$1.0M	Q2'15	$1.0M	Q4'15	$1.0M	Q3'16
IND clearance from the FDA	$4.0M	Q1'16	$4.0M	Q2'16	$4.0M	Q2'17
Phase 2 clinical trial initiation	$3.0M	Q2'17	$3.0M	Q4'17	—	—
Phase 3 clinical trial initiation	$5.0M	Q3'18	—	—	—	—

Milestones achieved through September 30, 2018 under the Celgene Agreement are as follows:



	Anti-PD-1 (CC-90006)
Milestone Event	Amount	Quarter Recognized
Completion of first in vivo toxicology studies using GLPs	$0.5M	Q2'16
Phase 1 clinical trial initiation	$1.0M	Q4'16

Fair Value Measurements and Available for Sale Investments (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of Assets and Liabilities that Require Fair Value Measurements on a Recurring Basis

The following table summarizes our assets and liabilities that require fair value measurements on a recurring basis and their respective input levels based on the fair value hierarchy:



	Fair Value Measurements at End of Period Using:
(in thousands)	Fair Value		Quoted Market Prices for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
At September 30, 2018
Money market funds⁽¹⁾	$	51,442	$	51,442	$	—	$	—
Mutual funds⁽¹⁾	236,332		236,332		—		—
U.S. treasury securities⁽²⁾	95,086		95,086		—		—
Certificates of deposit⁽²⁾	959		—		959		—
Agency securities⁽²⁾	44,647		—		44,647		—
Commercial and corporate obligations⁽¹⁾⁽²⁾	80,646		—		80,646		—
At December 31, 2017
Money market funds⁽¹⁾	$	41,318	$	41,318	$	—	$	—
Mutual funds⁽¹⁾	28,817		28,817		—		—
U.S. treasury securities⁽²⁾	79,397		79,397		—		—
Agency securities⁽²⁾	59,948		—		59,948		—
Commercial and corporate obligations⁽²⁾	111,660		—		111,660		—


⁽¹⁾	Included in cash and cash equivalents, and restricted cash in the accompanying consolidated balance sheets.


⁽²⁾	Included in short-term or long-term investments in the accompanying consolidated balance sheets depending on the respective maturity date.

Schedule of Weighted-average Assumptions for Liabilities for Series C Preferred Stock Warrants



	January 31, 2017
Fair value of preferred stock	$	16.95
Exercise price	$	4.55
Risk-free interest rate	1.4		%
Volatility	88.8		%
Dividend Yield	—		%
Contractual term (in years)	3.8
Weighted-average measurement date fair value per share	$	13.71

Summary of Activity in Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs

The following table summarizes the activity in liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3 Inputs):



	Nine Months Ended September 30,
(in thousands)	2017
Preferred Stock Warrant Liabilities:
Beginning balance	$	(3,241	)
Net gains (losses) included in other expense	(1,366		)
Reclassification of warrant liabilities to equity	4,607
Ending balance	$	—

Fair Value of Other Financial Instruments

The fair value of our other financial instruments estimated as of September 30, 2018 and December 31, 2017 are presented below:



	September 30, 2018				December 31, 2017
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Notes payable	$	9,909	$	10,671	$	14,428	$	15,650

Available-for-sale Investments

The aggregate market value, cost basis, and gross unrealized gains and losses of available-for-sale investments by security type, classified in cash equivalents, short-term and long-term investments as of September 30, 2018 are as follows:



(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Total Fair Value
Agency securities⁽¹⁾	$	44,832	$	—	$	(185	)	$	44,647
Certificates of deposit⁽²⁾	959		—		—			959
Commercial and corporate obligations⁽³⁾	80,812		1		(167		)	80,646
US Treasury securities⁽⁴⁾	95,276		—		(190		)	95,086
Total available-for-sale investments	$	221,879	$	1	$	(542	)	$	221,338


⁽¹⁾	Of our outstanding agency securities, $42.9 million have maturity dates of less than one year and $1.7 million have a maturity date of between one to two years as of September 30, 2018.


⁽²⁾	All of our outstanding certificates of deposit have a maturity date of between one to two years as of September 30, 2018.


⁽³⁾	Of our outstanding commercial and corporate obligations, $74.6 million have maturity dates of less than one year and $6.1 million have a maturity date of between one to two years as of September 30, 2018.


⁽⁴⁾	Of our outstanding U.S. Treasury securities $85.2 million have maturity dates of less than one year and $9.9 million have a maturity date of between one to two years as of September 30, 2018.

Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2018

Equity [Abstract]

Schedule of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance upon the exercise, issuance or conversion of the respective equity instruments at September 30, 2018 are as follows:



Issued and Outstanding:
Stock options	2,308,389
Shares Reserved For:
2017 Equity Incentive Plan	2,038,194
Employee Stock Purchase Plan	455,913
Total	4,802,496

Equity Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Activity Related to Stock Option Awards

A summary of the activity related to stock option awards during the nine months ended September 30, 2018 is as follows:



	Shares Subject to Options		Weighted-Average Exercise Price per Share		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at January 1, 2018	2,425,903		$	12.03
Granted	339,557		$	100.98
Exercises	(410,551	)	$	5.21
Forfeitures and cancellations	(46,520	)	$	49.68
Outstanding at September 30, 2018	2,308,389		$	25.57	7.25	$	173,085
Exercisable at September 30, 2018	1,330,540		$	10.62	6.27	$	118,779

Summary of Weighted Average Assumptions in Stock Option Valuations



	Nine Months Ended September 30,
	2018			2017
Risk-free interest rate	2.6		%	2.0		%
Expected volatility	68.0		%	64.4		%
Expected dividend yield	—		%	—		%
Expected term (in years)	6.25			6.25
Weighted average grant date fair value per share	$	63.49		$	22.54

Summary of Non-cash Stock-based Compensation Expense

Total non-cash stock-based compensation expense for all stock awards that was recognized in the consolidated statements of operations and comprehensive loss is as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2018		2017		2018		2017
Research and development	$	837	$	198	$	2,492	$	997
General and administrative	1,695		744		4,848		2,249
Total	$	2,532	$	942	$	7,340	$	3,246

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2018

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Annual Obligations

At September 30, 2018, the future minimum annual obligations under non-cancellable operating lease commitments are as follows:



Years Ending December 31, (in thousands)
2018	$	201
2019	938
2020	968
2021	726
2022	—
Thereafter	—
Total minimum payments required	$	2,833

Description of the Business (Details) $ / shares in Units, $ in Thousands						9 Months Ended
	Sep. 28, 2018 USD ($) $ / shares shares	Nov. 14, 2017 USD ($) $ / shares shares	Oct. 17, 2017 USD ($) $ / shares shares	Jan. 31, 2017 USD ($) $ / shares shares	Jan. 13, 2017	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jan. 30, 2017 shares
Class of Warrant or Right [Line Items]
Common shares issued during period (in shares)	2,530,000		3,000,000
Shares issued, share price (in dollars per share) \| $ / shares	$ 94.46		$ 68.50
Reverse stock split, conversion ratio					0.1429
Proceeds from issuance of stock, net of underwriters' fees \| $	$ 227,500		$ 194,700			$ 227,476	$ 80,213
Convertible preferred stock
Class of Warrant or Right [Line Items]
Number of shares called by warrants (in shares)								377,195
Common Stock
Class of Warrant or Right [Line Items]
Number of shares called by warrants (in shares)				377,195
IPO
Class of Warrant or Right [Line Items]
Proceeds from initial public offering, net of underwriters fees \| $				$ 80,200
IPO \| Common Stock
Class of Warrant or Right [Line Items]
Common shares issued during period (in shares)				5,750,000
Shares issued, share price (in dollars per share) \| $ / shares				$ 15.00
Convertible preferred stock, converted to common stock (in shares)				11,520,698
Underwriters' option
Class of Warrant or Right [Line Items]
Common shares issued during period (in shares)	330,000	271,380
Shares issued, share price (in dollars per share) \| $ / shares		$ 68.5
Proceeds from issuance of stock, net of underwriters' fees \| $		$ 17,600

Summary of Significant Accounting Policies - Additional Information (Details)	9 Months Ended
	Sep. 30, 2018 segment
Accounting Policies [Abstract]
Number of reportable segments	1

Summary of Significant Accounting Policies - Summary of Potentially Dilutive Securities (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share (in shares)	2,402	1,755	2,517	2,092
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share (in shares)	2,402	1,755	2,514	1,883
Warrants to purchase common stock \| Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share (in shares)	0	0	3	209

Balance Sheet Accounts and Supplemental Disclosures - Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,436	$ 4,643
Less: accumulated depreciation and amortization	(4,092)	(3,978)
Total property and equipment, net	1,344	665
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,138	3,687
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	723	605
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 575	$ 351

Balance Sheet Accounts and Supplemental Disclosures - Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Accrued compensation and related expenses	$ 2,176	$ 1,588
Accrued research and contract manufacturing expenses	4,196	2,961
Other	773	326
Total accrued expenses	$ 7,145	$ 4,875

Collaborative Research and Development Agreements (Details)	1 Months Ended		3 Months Ended										9 Months Ended		12 Months Ended
	Nov. 30, 2014 USD ($) target	Mar. 31, 2014 USD ($) target	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($) milestone	Dec. 31, 2011 USD ($)
Deferred Revenue Arrangement [Line Items]
Collaboration revenue			$ 5,000,000		$ 0								$ 5,000,000	$ 7,000,000
Milestones achieved during period, amount \| milestone														2
TESARO \| Collaborative Research And Development Agreement
Deferred Revenue Arrangement [Line Items]
Upfront license fee received	$ 2,000,000	$ 17,000,000
Number of outstanding research and development targets \| target	4	3
Milestone payments, contingent upon preclinical and clinical trial events (up to)	$ 18,000,000
Milestone payments, contingent upon certain U.S. and European regulatory submissions and approvals (up to)	90,000,000
Milestone payments, contingent upon achievement of specified levels of worldwide sales (up to)	$ 165,000,000
Agreement term following first commercial sale or expiration of the last to expire patent (in years)	12 years
Collaboration revenue			5,000,000		0								5,000,000	$ 7,000,000
TESARO \| Initiated in vivo toxicology studies using good laboratory practices (GLPs) \| AnaptysBio-generated Anti-PD-1 Antagonist Antibody (TSR-042)
Deferred Revenue Arrangement [Line Items]
Milestones achieved, amount												$ 1,000,000
TESARO \| Initiated in vivo toxicology studies using good laboratory practices (GLPs) \| AnaptysBio Generated Anti-TIM3 Antagonist Antibody (TSR-022)
Deferred Revenue Arrangement [Line Items]
Milestones achieved, amount											$ 1,000,000
TESARO \| Initiated in vivo toxicology studies using good laboratory practices (GLPs) \| AnaptysBio Generated Anti-LAG3 Antagonist Antibody (TSR-033)
Deferred Revenue Arrangement [Line Items]
Milestones achieved, amount								$ 1,000,000
TESARO \| IND clearance from the FDA \| AnaptysBio-generated Anti-PD-1 Antagonist Antibody (TSR-042)
Deferred Revenue Arrangement [Line Items]
Milestones achieved, amount										$ 4,000,000
TESARO \| IND clearance from the FDA \| AnaptysBio Generated Anti-TIM3 Antagonist Antibody (TSR-022)
Deferred Revenue Arrangement [Line Items]
Milestones achieved, amount									$ 4,000,000
TESARO \| IND clearance from the FDA \| AnaptysBio Generated Anti-LAG3 Antagonist Antibody (TSR-033)
Deferred Revenue Arrangement [Line Items]
Milestones achieved, amount						$ 4,000,000
TESARO \| Phase 2 clinical trial initiation \| AnaptysBio-generated Anti-PD-1 Antagonist Antibody (TSR-042)
Deferred Revenue Arrangement [Line Items]
Milestones achieved, amount						$ 3,000,000
TESARO \| Phase 2 clinical trial initiation \| AnaptysBio Generated Anti-TIM3 Antagonist Antibody (TSR-022)
Deferred Revenue Arrangement [Line Items]
Milestones achieved, amount				$ 3,000,000
TESARO \| Phase 3 clinical trial initiation \| AnaptysBio-generated Anti-PD-1 Antagonist Antibody (TSR-042)
Deferred Revenue Arrangement [Line Items]
Milestones achieved, amount			5,000,000
Celgene Corporation \| Collaborative Research And Development Agreement
Deferred Revenue Arrangement [Line Items]
Upfront license fee received															$ 6,000,000
Collaboration revenue			$ 0		$ 0								$ 0	$ 0
Maximum milestone payments per target															$ 53,000,000
Celgene Corporation \| Initiated in vivo toxicology studies using good laboratory practices (GLPs) \| AnaptysBio-Generated Anti-PD-1 Antagonist Antibody (CC-90006)
Deferred Revenue Arrangement [Line Items]
Milestone payment earned									$ 500,000
Celgene Corporation \| Phase 1 clinical trial initiation \| AnaptysBio-Generated Anti-PD-1 Antagonist Antibody (CC-90006)
Deferred Revenue Arrangement [Line Items]
Milestone payment earned							$ 1,000,000

Notes Payable (Details)		1 Months Ended
Notes Payable (Details)	Dec. 24, 2014 USD ($) installment $ / shares shares	Jan. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) payment	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Notes payable, current portion			$ 7,500,000	$ 6,875,000
Term A Loan Warrants \| Warrants to purchase common stock
Debt Instrument [Line Items]
U.S. treasury securities	$ 100,000
Term A Loan Warrants \| Warrants to purchase common stock \| Measurement Input, Price Volatility (as a percent)
Debt Instrument [Line Items]
Measurement Input (as a percent)	0.702
Term A Loan Warrants \| Warrants to purchase common stock \| Measurement Input, Expected Term
Debt Instrument [Line Items]
Contractual term (in years)	10 years
Term A Loan Warrants \| Warrants to purchase common stock \| Measurement Input, Risk Free Interest Rate
Debt Instrument [Line Items]
Measurement Input (as a percent)	0.0197
Term B And C Loans Warrants \| Warrants to purchase common stock
Debt Instrument [Line Items]
U.S. treasury securities		$ 900,000
Term B And C Loans Warrants \| Warrants to purchase common stock \| Measurement Input, Price Volatility (as a percent)
Debt Instrument [Line Items]
Measurement Input (as a percent)		0.792
Term B And C Loans Warrants \| Warrants to purchase common stock \| Measurement Input, Expected Term
Debt Instrument [Line Items]
Contractual term (in years)		10 years
Term B And C Loans Warrants \| Warrants to purchase common stock \| Measurement Input, Risk Free Interest Rate
Debt Instrument [Line Items]
Measurement Input (as a percent)		0.0245
Series C Preferred Stock \| Term A Loan Warrants
Debt Instrument [Line Items]
Number of shares called by warrants (in shares) \| shares	41,208
Warrant exercise price (in dollars per share) \| $ / shares	$ 4.55
Series C Preferred Stock \| Term B And C Loans Warrants
Debt Instrument [Line Items]
Number of shares called by warrants (in shares) \| shares		82,416
Warrant exercise price (in dollars per share) \| $ / shares		$ 4.55
Notes Payable to Banks
Debt Instrument [Line Items]
Aggregate borrowing capacity	$ 5,000,000
Notes Payable to Banks \| Loan and Security Agreement (LSA)
Debt Instrument [Line Items]
Debt instrument, maximum borrowing capacity	$ 15,000,000
Number of loan installments (in installments) \| installment	3
Final payment fee		$ 800,000
Notes payable			9,900,000
Debt instrument discounts			100,000
Notes payable, current portion			$ 7,500,000
Effective interest rate			13.08%
Long-term Debt, Fiscal Year Maturity [Abstract]
Debt maturities in remainder of year			$ 1,900,000
2019			7,500,000
2020			$ 600,000
Notes Payable to Banks \| Term A Loans
Debt Instrument [Line Items]
Aggregate draw on term loan	$ 5,000,000
Fixed interest rate (as a percent)	6.97%
Notes Payable to Banks \| Term B and Term C Loans
Debt Instrument [Line Items]
Aggregate borrowing capacity		$ 10,000,000
Number of principal and interest payments (in payments) \| payment			16
Notes Payable to Banks \| Term B Loans
Debt Instrument [Line Items]
Fixed interest rate (as a percent)	6.97%	7.30%
Interest rate at period end (as a percent)			8.69%
Notes Payable to Banks \| Term B Loans \| 3-Month LIBOR interest rate
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)		6.37%
Notes Payable to Banks \| Term C Loans
Debt Instrument [Line Items]
Fixed interest rate (as a percent)	6.97%	7.30%
Interest rate at period end (as a percent)			8.69%
Notes Payable to Banks \| Term C Loans \| 3-Month LIBOR interest rate
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)		6.37%

Fair Value Measurements and Available for Sale Investments - Fair Value Assumptions (Details) - Fair Value, Measurements, Recurring - Derivative Financial Instruments, Liabilities - Series C Preferred Stock	Jan. 31, 2017 $ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value of preferred stock (in dollars per share)	$ 16.95
Weighted-average measurement date fair value per share (in dollars per share)	$ 13.71
Measurement Input, Exercise Price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	4.55
Measurement Input, Risk Free Interest Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.014
Measurement Input, Option Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.888
Measurement Input, Expected Dividend Rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0
Measurement Input, Expected Term
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contractual term (in years)	3 years 9 months

Fair Value Measurements and Available for Sale Investments - Liabilities with Significant Unobservable Inputs (Details) - Series C Preferred Stock - Derivative Financial Instruments, Liabilities - Fair Value, Measurements, Recurring $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (3,241)
Net gains (losses) included in other expense	(1,366)
Reclassification of warrant liabilities to equity	4,607
Ending balance	$ 0

Fair Value Measurements and Available for Sale Investments - Fair Value of Other Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	$ 9,909	$ 14,428
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	$ 10,671	$ 15,650

Fair Value Measurements and Available for Sale Investments - Available-for-sale Investments (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 221,879
Gross Unrealized Gains	1
Gross Unrealized Losses	(542)
Total Fair Value	221,338
Short-term investments	200,406	$ 167,218
Long-term investments	18,616	$ 75,897
Agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	44,832
Gross Unrealized Gains	0
Gross Unrealized Losses	(185)
Total Fair Value	44,647
Short-term investments	42,900
Long-term investments	1,700
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	959
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Total Fair Value	$ 959
Certificates of deposit \| Minimum
Debt Securities, Available-for-sale [Line Items]
Investments outstanding, maturity date range (in years)	1 year
Certificates of deposit \| Maximum
Debt Securities, Available-for-sale [Line Items]
Investments outstanding, maturity date range (in years)	2 years
Commercial and corporate obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 80,812
Gross Unrealized Gains	1
Gross Unrealized Losses	(167)
Total Fair Value	80,646
Short-term investments	74,600
Long-term investments	$ 6,100
Commercial and corporate obligations \| Minimum
Debt Securities, Available-for-sale [Line Items]
Investments outstanding, maturity date range (in years)	1 year
Commercial and corporate obligations \| Maximum
Debt Securities, Available-for-sale [Line Items]
Investments outstanding, maturity date range (in years)	2 years
U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 95,276
Gross Unrealized Gains	0
Gross Unrealized Losses	(190)
Total Fair Value	95,086
Short-term investments	85,200
Long-term investments	$ 9,900
U.S. treasury securities \| Minimum
Debt Securities, Available-for-sale [Line Items]
Investments outstanding, maturity date range (in years)	1 year
U.S. treasury securities \| Maximum
Debt Securities, Available-for-sale [Line Items]
Investments outstanding, maturity date range (in years)	2 years

Stockholders' Equity - Additional Information (Details) - $ / shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jan. 31, 2017
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	500,000,000		500,000,000	500,000,000
Common stock, par value (in dollars per share)	$ 0.001		$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000		0	10,000,000
Preferred stock, par value (in dollars per share)	$ 0.001		$ 0.001	$ 0.001
Common stock, shares issued (in shares)	26,748,713		23,791,000
Common stock, shares outstanding (in shares)	26,748,713		23,791,000
Common Stock
Class of Stock [Line Items]
Warrants exercised, number of shares represented (as shares)	16,770	476,251
Warrants exercised, number of shares represented, cashless exercise (as shares)		358,342
Shares issued as a result of warrants exercised (in shares)		397,445

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Details) - shares	Sep. 30, 2018	Dec. 31, 2017
Issued and Outstanding:
Stock options outstanding (in shares)	2,308,389	2,425,903
Common stock, shares reserved for issuance (in shares)	4,802,496
2017 Equity Incentive Plan
Issued and Outstanding:
Shares reserved for future award grants (in shares)	2,038,194
Employee Stock Purchase Plan
Issued and Outstanding:
Shares reserved for future award grants (in shares)	455,913

Equity Incentive Plans - Narrative (Details) - USD ($) $ in Thousands			9 Months Ended
	Jan. 01, 2018	Jan. 26, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of common stock, upon the exercise of stock options			$ 2,138	$ 814
Unrecognized compensation cost			$ 27,800
Employee and Nonemployee Stock Options vesting period (in years)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)		4 years
Award expiration period (in years)		10 years
Weighted average period remaining for amortization of unrecognized compensation cost (in years)			2 years 5 months 14 days
Options to purchase common stock \| Director Stock options vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)		1 year
Award expiration period (in years)		10 years
Options to purchase common stock \| Non-Employee Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)			3 years
2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increase in number of shares available for issuance		4.00%
Capital shares reserved for future issuance, increase (in shares)	951,656
Employee Stock Purchase Plan \| Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increase in number of shares available for issuance	1.00%
Capital shares reserved for future issuance, increase (in shares)	237,913

Equity Incentive Plans - Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Shares Subject to Options
Stock options outstanding, beginning balance (in shares)	2,425,903
Granted (in shares)	339,557	1,061,106
Exercises (in shares)	(410,551)
Forfeitures and cancellations (in shares)	(46,520)
Stock options outstanding, ending balance (in shares)	2,308,389
Stock options exercisable, ending balance (in shares)	1,330,540
Weighted-Average Exercise Price per Share
Stock options outstanding, beginning balance (in dollars per share)	$ 12.03
Granted (in dollars per share)	100.98
Exercises (in dollars per share)	5.21
Forfeitures and cancellations (in dollars per share)	49.68
Stock options outstanding, ending balance (in dollars per share)	25.57
Stock options exercisable, ending balance (in dollars per share)	$ 10.62
Weighted-Average Remaining Contractual Term and Aggregate Intrinsic Value
Weighted average remaining contractual term, options outstanding (in years)	7 years 3 months 1 day
Weighted average remaining contractual term, options exercisable (in years)	6 years 3 months 9 days
Aggregate intrinsic value, options outstanding	$ 173,085
Aggregate intrinsic value, options exercisable	$ 118,779

Equity Incentive Plans - Option Fair Value Assumptions (Details) - Options to purchase common stock - $ / shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.60%	2.00%
Expected volatility	68.00%	64.40%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	6 years 3 months	6 years 3 months
Weighted average grant date fair value per share (in dollars per share)	$ 63.49	$ 22.54

Equity Incentive Plans - Allocation of Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 2,532	$ 942	$ 7,340	$ 3,246
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	837	198	2,492	997
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 1,695	$ 744	$ 4,848	$ 2,249

Australia Research and Development Tax Incentive (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Australian tax incentive receivable	$ 173		$ 173		$ 1,601
Research and development tax incentive credit received during the period			$ 1,500	$ 4,600
Australian Taxation Office \| Subsidiaries
Tax Credit Carryforward [Line Items]
Refundable tax incentive for qualified research and development activities (as a percent)			43.50%		43.50%
Research and development	$ 100	$ 200	$ 100	$ 1,400

Commitments and Contingencies (Details) ft² in Thousands, $ in Thousands	1 Months Ended
	May 31, 2018 ft²	Sep. 30, 2018 USD ($)	Dec. 31, 2015
Operating Leased Assets [Line Items]
2018		$ 201
2019		938
2020		968
2021		726
2022		0
Thereafter		0
Total minimum payments required		$ 2,833
New Sub-lease Agreement
Operating Leased Assets [Line Items]
Operating lease, term of contract	3 years
Operating lease, rented square feet (in square feet) \| ft²	18
Original Sub-lease Agreement
Operating Leased Assets [Line Items]
Operating lease, renewal term			5 years

Fair Value Measurements and Available for Sale Investments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	$ 221,338
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	95,086
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	959
Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	44,647
Commercial and corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	80,646
Fair Value, Measurements, Recurring \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	95,086	$ 79,397
Fair Value, Measurements, Recurring \| Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	959
Fair Value, Measurements, Recurring \| Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	44,647	59,948
Fair Value, Measurements, Recurring \| Commercial and corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	80,646	111,660
Fair Value, Measurements, Recurring \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	51,442	41,318
Fair Value, Measurements, Recurring \| Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	236,332	28,817
Fair Value, Measurements, Recurring \| Quoted Market Prices for Identical Assets (Level 1) \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	95,086	79,397
Fair Value, Measurements, Recurring \| Quoted Market Prices for Identical Assets (Level 1) \| Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	0
Fair Value, Measurements, Recurring \| Quoted Market Prices for Identical Assets (Level 1) \| Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	0	0
Fair Value, Measurements, Recurring \| Quoted Market Prices for Identical Assets (Level 1) \| Commercial and corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	0	0
Fair Value, Measurements, Recurring \| Quoted Market Prices for Identical Assets (Level 1) \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	51,442	41,318
Fair Value, Measurements, Recurring \| Quoted Market Prices for Identical Assets (Level 1) \| Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	236,332	28,817
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	0	0
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	959
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	44,647	59,948
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Commercial and corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	80,646	111,660
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0	0
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0	0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	0	0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	0	0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Commercial and corporate obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt securities	0	0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	0	0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	$ 0	$ 0