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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2017	May 09, 2017
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	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		20,269,273

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 96,754	$ 51,232
Receivable from collaborative partners	0	1,225
Australian tax incentive receivable	4,965	4,118
Short-term investments	6,742	0
Prepaid expenses and other current assets	1,694	1,633
Total current assets	110,155	58,208
Property and equipment, net	569	471
Long-term investments	20,327	0
Restricted cash	60	60
Deferred financing costs	0	3,441
Total assets	131,111	62,180
Current liabilities:
Accounts payable	2,546	2,278
Accrued expenses	4,330	3,429
Notes payable, current portion	1,250	0
Other current liabilities	0	1
Total current liabilities	8,126	5,708
Notes payable, net of current portion	12,709	13,809
Deferred rent	161	154
Preferred stock warrant liabilities	0	3,241
Commitments and contingencies
Stockholders’ equity (deficit):
Preferred stock, $0.001 par value, 10,000 shares and no shares authorized, issued or outstanding at March 31, 2017 and December 31, 2016, respectively	0	0
Common stock, $0.001 par value, 500,000 and 17,214 authorized, 20,249 shares and 2,651 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	20	3
Additional paid in capital	176,507	16,672
Accumulated other comprehensive income (loss)	(13)	0
Accumulated deficit	(66,399)	(54,923)
Total stockholders’ equity (deficit)	110,115	(38,248)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	131,111	62,180
Series B convertible preferred stock
Current liabilities:
Convertible preferred stock	0	28,220
Series C convertible preferred stock
Current liabilities:
Convertible preferred stock	0	6,452
Series C-1 convertible preferred stock
Current liabilities:
Convertible preferred stock	0	2,156
Series D convertible preferred stock
Current liabilities:
Convertible preferred stock	$ 0	$ 40,688

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016
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	17,214,000
Common stock, shares issued (in shares)	20,249,295	2,651,000
Common stock, shares outstanding (in shares)	20,249,295	2,651,000
Series B convertible preferred stock
Convertible preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized (in shares)	0	3,963,000
Convertible preferred stock, shares issued (in shares)	0	3,963,000
Convertible preferred stock, shares outstanding (in shares)	0	3,963,000
Series C convertible preferred stock
Convertible preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized (in shares)	0	1,887,000
Convertible preferred stock, shares issued (in shares)	0	1,593,000
Convertible preferred stock, shares outstanding (in shares)	0	1,593,000
Series C-1 convertible preferred stock
Convertible preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized (in shares)	0	474,000
Convertible preferred stock, shares issued (in shares)	0	474,000
Convertible preferred stock, shares outstanding (in shares)	0	474,000
Series D convertible preferred stock
Convertible preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized (in shares)	0	5,491,000
Convertible preferred stock, shares issued (in shares)	0	5,491,000
Convertible preferred stock, shares outstanding (in shares)	0	5,491,000

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Collaboration revenue	$ 0	$ 4,866
Operating expenses:
Research and development	7,935	4,786
General and administrative	2,053	1,219
Total operating expenses	9,988	6,005
Loss from operations	(9,988)	(1,139)
Other income (expense), net
Interest expense	(428)	(115)
Change in fair value of liability for preferred stock warrants	(1,366)	379
Other income (expense), net	347	(13)
Total other income (expense), net	(1,447)	251
Net loss	(11,435)	(888)
Unrealized loss on available for sale securities	(13)	0
Other comprehensive loss	(13)	0
Comprehensive loss	$ (11,448)	$ (888)
Net loss per common share:
Basic and diluted (in dollars per share)	$ (0.75)	$ (0.34)
Weighted-average number of shares outstanding:
Basic and diluted (in shares)	15,295	2,629

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (11,435)	$ (888)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	39	57
Stock-based compensation	866	322
Change in fair value of liability for preferred stock warrants	1,366	(379)
Noncash interest expense	150	22
Changes in operating assets and liabilities:
Receivable from collaborative partners	1,225	35
Australian tax incentive receivable	(847)	0
Prepaid expenses and other assets	(143)	(316)
Accounts payable and other liabilities	682	(1,093)
Income taxes payable	0	(139)
Deferred revenue	0	323
Net cash used in operating activities	(8,097)	(2,056)
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisition of investments	(27,000)	0
Purchases of property and equipment	(85)	(35)
Net cash used in investing activities	(27,085)	(35)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from initial public offering, net of underwriters fees	80,213	0
Proceeds from issuance of common stock, upon the exercise of stock options	355	9
Proceeds from issuance of common stock, upon the exercise of warrants	535	0
Payments for repurchase of common stock	0	(1)
Payments for offering costs	(399)	(283)
Net cash provided by (used in) financing activities	80,704	(275)
Net increase (decrease) in cash, cash equivalents, and restricted cash	45,522	(2,366)
Cash, cash equivalents and restricted cash, beginning of period	51,292	51,744
Cash, cash equivalents and restricted cash, end of period	96,814	49,378
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Interest paid	278	87
Noncash investing and financing activities:
Amounts accrued for property and equipment	52	7
Amounts accrued for offering costs	1,290	260
Reclassification of warrants to equity	$ 4,607	$ 0

Description of the Business

3 Months Ended

Mar. 31, 2017

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 our collaborative research and development arrangements.

Since our inception, we have devoted our primary effort to raising capital and research and development activities, and at March 31, 2017, have an accumulated deficit of $66.4 million. Through March 31, 2017, all of our financial support has been provided primarily from the sale of our common and preferred stock, proceeds from the issuance of convertible debt and funds received under our collaborative research and development agreements. 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. The accompanying consolidated financial statements do not include any adjustments that might be necessary if we are unable to continue as a going concern.

Initial Public Offering and Related Transactions

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.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2017

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 (“SEC”). Certain information and note disclosures normally included in annual financial statements prepared in accordance with U.S. generally accepted accounting principles (“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 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 months ended March 31, 2017 are not necessarily indicative of the results that may be expected for the year ending December 31, 2017. The financial statements should be read in conjunction with our audited financial statements for the year ended December 31, 2016, included in our Annual Form 10-K.

Basis of Consolidation

The accompanying consolidated financial statements include us and our wholly-owned Australian subsidiary, which was established in March 2015. All intercompany accounts and transactions have been eliminated in consolidation. We operate in one reportable segment in the United States of America 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.

Short Term and Long Term Investments

All investments have been classified as “available-for-sale” and are carried at fair value as determined based upon quoted market prices or pricing models for similar securities at period end. Investments with contractual maturities less than 12 months at the balance sheet date are considered short-term investments. Those investments with contractual maturities greater than 12 months at the balance sheet date are considered long-term investments. Unrealized gains and losses, deemed temporary in nature, are reported as a component of accumulated other comprehensive income (loss), net of tax. A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the security. Premiums (discounts) are amortized (accreted) over the life of the related security as an adjustment to yield using the straight-line interest method. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold.

Concentration of Credit Risk

Financial instruments that potentially subject us to a concentration of credit risk consist of cash and cash equivalents and certain investments in money market funds, agency securities, commercial paper and U.S. treasury securities. Bank deposits are diversified between three financial institutions and these deposits may exceed insured limits. We are exposed to credit risk in the event of default by the financial institutions holding our cash and cash equivalents and issuers of investments that are recorded on our consolidated balance sheets. We mitigate our risk by investing in high-grade instruments and limiting the concentration in any one issuer, which limits our exposure.

Comprehensive Loss

Comprehensive loss represents all changes in stockholders’ equity (deficit) except those resulting from distributions to stockholders. Our unrealized losses on investments represent the only component of other comprehensive loss that is excluded from the reported net loss.

Net Income (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 all periods 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 March 31,
(in thousands)	2017	2016
Convertible preferred stock	—	11,521
Options to purchase common stock	1,995	2,027
Warrants to purchase preferred stock	—	294
Warrants to purchase common stock	332	117
Total	2,327	13,959

Accounting Pronouncements Recently Adopted

In March 2016, the FASB issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. Under the new guidance, additional paid-in capital pools will be eliminated and entities will be required to recognize the income tax effects of share-based awards in the income statement when share-based awards vest or are settled. ASU 2016-09 also changes the classification of excess tax benefits on the statement of cash flows. It also will allow an employer to repurchase more of an employee's shares than it can currently for tax withholding purposes without triggering liability accounting and to make a policy election to either account for forfeitures as they occur or to continue the current practice of estimating forfeitures at the time of grant. ASU 2016-09 became effective for annual reporting periods beginning January 1, 2017, including interim periods thereafter. Upon adoption of this standard in January 2017, we recognized a cumulative increase of $41,000 to our accumulated deficit as a result of a change in accounting policy, due to our transition from calculating an estimated forfeiture rate at grant date to recording actual forfeitures as they occur. We did not record any other adjustments upon adoption of this standard.

In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, which requires companies to include cash and cash equivalents that have restrictions on withdrawal or use in total cash and cash equivalents on the statement of cash flows. ASU 2016-18 becomes effective for annual reporting periods beginning January 1, 2018, including interim periods thereafter; early adoption is permitted, including adoption in an interim period. Upon early adoption of this standard in January 2017, we adjusted our consolidated statement of cash flows to include $60,000 in restricted cash in the beginning and ending cash balance. We did not record any other adjustments upon adoption of this standard.

Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“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 becomes effective for our annual reporting period beginning January 1, 2018, including interim periods within that reporting period; adoption is permitted as early as January 1, 2017. Entities have the option of using either a full retrospective or a modified retrospective approach for the adoption of the new standard. We will transition this standard using the modified retrospective approach for our annual reporting period beginning January 1, 2018. While we are continuing to assess all potential impacts of the standard, we currently believe the most significant impact relates to our accounting for variable consideration including revenues related to contingent “milestone” based payments. 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, given the nature of potential milestones owed to us, and the inherent risk involved in developing drugs, we believe that the majority of potential milestones will not be recognizable as of the standard adoption date.

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 becomes effective for our annual reporting period beginning January 1, 2018, including interim periods within that reporting period; early adoption is permitted. We are currently assessing the impact that this standard will have on our consolidated financial statements.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires that lessees recognize a right-of-use asset and a related lease liability arising from leases on the balance sheet. ASU 2016-02 becomes effective for our annual reporting period beginning January 1, 2019, including interim periods thereafter; early adoption is permitted. We are currently reviewing all contracts outstanding and are assessing the impact that this standard will have on our consolidated financial statements.

Balance Sheet Accounts and Supplemental Disclosures

3 Months Ended

Mar. 31, 2017

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Accounts and Supplemental Disclosures

Property and Equipment

Property and equipment consist of the following:



(in thousands)	March 31, 2017			December 31, 2016
Laboratory equipment	$	3,460		$	3,383
Office furniture and equipment	595			535
Leasehold improvements	351			351
	4,406			4,269
Less: accumulated depreciation and amortization	(3,837		)	(3,798		)
Total property and equipment, net	$	569		$	471

Accrued Expenses

Accrued expenses consist of the following:



(in thousands)	March 31, 2017		December 31, 2016
Accrued compensation and related expenses	$	659	$	973
Accrued professional fees	137		296
Accrued research and contract manufacturing expenses	3,423		2,084
Other	111		76
Total accrued expenses	$	4,330	$	3,429

Collaborative Research and Development Agreements	3 Months Ended
Collaborative Research and Development Agreements	Mar. 31, 2017
Revenue Recognition [Abstract]
Collaborative Research and Development Agreements	Collaborative Research and Development Agreements TESARO Collaboration In March 2014, we entered into a Collaboration and Exclusive License Agreement (TESARO Agreement) with TESARO, Inc. and TESARO Development, Inc. (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 an 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 later of the 12th anniversary of the first commercial sale of the product or the expiration of the last to expire of any patent. 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. During the year ended December 31, 2015, we achieved two $1.0 million milestones upon initiation of in vivo toxicology studies, using good laboratory practices (GLPs), for an AnaptysBio-generated anti-PD-1 antagonist antibody (TSR-042) and an AnaptysBio-generated anti-TIM-3 antagonist antibody (TSR-022), each being advanced by TESARO, for which we recognized $77,000 during the three months ended March 31, 2016. In January 2016, TESARO received clearance of their IND from the FDA for an AnaptysBio-generated anti-PD-1 antagonist antibody (TSR-042) resulting in us earning a $4.0 million milestone payment. We recognized $2.9 million of the $4.0 million milestone payment as revenue during the three months ended March 31, 2016. The $4.0 million milestone payment was received in February 2016. Revenue from future contingent milestone payments will be recognized if and when such payments become due, subject to satisfaction of all of the criteria necessary to recognize revenue at that time. We recognized no revenue under this agreement during the three months ended March 31, 2017. Revenue recognized under this agreement aggregated $4.9 million during the three months ended March 31, 2016, which includes $3.0 million related to milestones earned, $1.2 million in funding for research and development services and $0.7 million for the amortization of the upfront fee. Antibody Generation Agreement with Celgene Corporation In December 2011, we entered into a license and collaboration agreement with Celgene 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. There was no revenue recognized under this agreement during the three months ended March 31, 2017 and 2016.

Notes Payable	3 Months Ended
Notes Payable	Mar. 31, 2017
Debt Disclosure [Abstract]
Notes Payable	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 and each bear a fixed rate of interest of 6.97%. The Term B Loans for an aggregate of $5.0 million were initially available for draw through December 31, 2015, contingent upon our first multi-dose PK/toxicology studies on at least two development programs and the Term C Loans for an aggregate of $5.0 million were initially available for draw through December 31, 2016, contingent upon receiving FDA approval on IND submission on at least two development programs. The costs incurred to issue the Term A Loans of $85,000 were deferred and are included in the discount to the carrying value of the Term A Loans in the accompanying balance sheet. The Term A Loans also include a final payment fee of $0.3 million due at the earlier of prepayment or the maturity date of the Term A 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. 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, which are subject to change under anti-dilution provisions. The warrants are exercisable at any time through December 2024. 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. If the Term B Loans and Term C Loans were issued, they would bear interest at the greater of 6.95% or the 3-month LIBOR plus 6.72%, with principal payments beginning February 1, 2017 and with final maturity in January 2019. 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. As of March 31, 2017, the Term Loans are due in 10 monthly interest-only payments through January 2018, followed by 24 equal monthly principal and interest payments beginning February 1, 2018, with final maturity in January 2020. Each Loan bears interest equal to the greater of 3-month U.S. LIBOR plus 6.37% or 7.3%. The interest rate was 7.43% as of March 31, 2017. 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, which are subject to change under anti-dilution provisions. The warrants are exercisable at any time through December 2026. 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 7 below, 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. As of March 31, 2017, the carrying amount of the Term Loans were $14.0 million, which is net of discounts of $1.0 million and of which $1.3 million is classified as current liabilities as of March 31, 2017. The effective interest rate on the Term Loans at March 31, 2017 was 11.82%. As of March 31, 2017, future principal maturities of the Term Loans were $6.9 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 March 31, 2017, we were in compliance with the covenants contained in the Loan Agreement.

Fair Value Measurements and Available for Sale Investments

3 Months Ended

Mar. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements and Available for Sale Investments

Our financial instruments consist principally of cash, cash equivalents, restricted cash, short-term and long-term investments, receivables, accounts payable, notes payable and 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 March 31, 2017
Money market funds⁽¹⁾	$	83,309	$	83,309	$	—	$	—
Mutual funds⁽¹⁾	11,822		11,822		—		—
U.S. treasury securities⁽²⁾	4,982		4,982		—		—
Agency securities⁽²⁾	10,411		—		10,411		—
Commercial paper⁽³⁾	13,286		—		13,286		—
At December 31, 2016
Money market funds⁽¹⁾	$	31,955	$	31,955	$	—	$	—
Mutual funds⁽¹⁾	17,620		17,620		—		—
Preferred stock warrant liabilities	3,241		—		—		3,241


⁽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.


⁽³⁾	Included in cash and cash equivalents, short-term or long-term investments in the accompanying consolidated balance sheets depending on the respective maturity date.

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

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 requires Level 3 inputs.

As discussed in Note 7 below, 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 subsequent remeasurement using the Black-Scholes option-pricing model at each reporting date.

Estimating fair values of derivative financial instruments, including Level 3 instruments, require 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 employed 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, and December 31, 2016:



	January 31, 2017			December 31, 2016
Fair value of preferred stock	$	16.95		$	12.67
Exercise price	$	4.55		$	4.55
Risk-free interest rate	1.4		%	1.5		%
Volatility	88.8		%	88.6		%
Dividend Yield	—		%	—		%
Contractual term (in years)	3.8			3.8
Weighted-average measurement date fair value per share	$	13.71		$	9.65

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



	Three Months Ended March 31,
(in thousands)	2017			2016
Preferred Stock Warrant Liabilities:
Beginning balance	$	(3,241	)	$	(1,549	)
Net gains (losses) included in other expense	(1,366		)	379
Reclassification of warrant liabilities to equity	4,607			—
Ending balance	$	—		$	(1,170	)

Fair Value of Other Financial Instruments

The fair value of our financial instruments estimated as of March 31, 2017 and December 31, 2016 are presented below:



	March 31, 2017				December 31, 2016
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Notes payable	$	13,959	$	15,527	$	13,809	$	15,531

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.

Investments

In February 2017 we began investing our excess cash in agency securities, commercial paper and debt instruments of financial institutions and corporations, 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 March 31, 2017 are as follows:



(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Total Fair Value
Agency securities⁽¹⁾	$	10,416	$	1	$	(6	)	$	10,411
Commercial paper⁽²⁾	13,288		1		(3		)	13,286
US treasury securities⁽³⁾	4,988		—		(6		)	4,982
Total available-for-sale investments	$	28,692	$	2	$	(15	)	$	28,679


⁽¹⁾	Agency securities have a maturity date of between one to two years as of March 31, 2017.


⁽²⁾	Of our outstanding Commercial paper, $8.4 million have maturity dates of less than one year and $4.9 million have maturity dates of between one to two years as of March 31, 2017.


⁽³⁾	Treasury securities have a maturity date of between one to two years as of March 31, 2017.

- 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

3 Months Ended

Mar. 31, 2017

Equity [Abstract]

Stockholders' Equity

Stockholders’ Equity

Common and Preferred Stock

On January 13, 2017, we amended our Certificate of Incorporation to increase the number of authorized shares of common stock to 60,000,000 with a par value of $0.001 per share and decrease the number of authorized shares of preferred stock to 11,520,698 with a par value of $0.001 per share. Subsequently, 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 preferred shares of common 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, 20,249,295 shares were issued and outstanding as of March 31, 2017. Common stock reserved for future issuance upon the exercise, issuance or conversion of the respective equity instruments at March 31, 2017 are as follows:



Issued and Outstanding:
Stock options	2,722,883
Warrants for shares of common stock	198,009
Shares reserved for future award grants	1,204,923
Total	4,125,815

Warrant Exercises

Through March 31, 2017, warrants for the purchase of 296,669 shares of common stock were exercised, of which 179,047 were exercised by a net exercise method. As a result, we issued 250,448 shares of common stock, net.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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+ Details

Equity Incentive Plans

3 Months Ended

Mar. 31, 2017

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. A total of 1,955,506 shares of common stock were initially reserved for issuance under the 2017 plan, including 308,343 that were rolled over from the 2006 Plan. In addition, the number 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.

As of March 31, 2017, there were 2,722,883 options outstanding to purchase shares of common stock and 1,204,923 shares of common stock reserved for future stock awards under the 2017 Plan.

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 up the execution and delivery of the underwriting agreement for our initial public offering on January 26, 2017. A total of 218,000 shares of common stock are initially reserved for issuance under the ESPP. 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.

Stock Options

Stock options granted to employees and nonemployees generally vest over a four-year period while stock options granted to directors vest over a one 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 three months ended March 31, 2017 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, 2017	1,879,428		$	4.34
Granted	934,141		$	22.13
Exercises	(76,863	)	$	4.63
Forfeitures and cancellations	(13,823	)	$	7.15
Outstanding at March 31, 2017	2,722,883		$	10.42	8.15	$	47,184.0

Total cash received from the exercise of stock options was approximately $0.4 million during the three months ended March 31, 2017. As a result of the adoption of ASU 2016-09 and the elimination of a forfeiture rate as discussed in Note 2 above, all options outstanding are considered expected to vest.

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:



	Three Months Ended March 31, 2017
Risk-free interest rate	1.96		%
Expected volatility	77.64		%
Expected dividend yield	—		%
Expected term (in years)	6.18
Weighted average grant date fair value per share	$	15.15

There were 934,141 and no stock options granted during the three months ended March 31, 2017 and 2016, respectively.

We determine the appropriate, risk free interest rate, expected term for employee stock based awards, contractual term for nonemployee 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 nonemployee stock based awards is the remaining contractual life of the award. Estimated volatility incorporates historical volatility of 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.

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 March 31,
(in thousands)	2017		2016
Research and development	$	300	$	109
General and administrative	566		213
Total	$	866	$	322

At March 31, 2017, there was $16.7 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 3.1 years.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Australia Research and Development Tax Incentive	3 Months Ended
Australia Research and Development Tax Incentive	Mar. 31, 2017
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% and 45.0% refundable tax incentive for qualified research and development activities during fiscal 2017 and fiscal 2016, respectively. For the three months ended March 31, 2017, $0.6 million was recorded as a reduction to research and development expenses in the consolidated statements of operations and comprehensive loss. As of March 31, 2016, we had not yet determined that we would meet the eligibility criteria for fiscal 2016, and therefore did not record a reduction to research and development expense.

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events In April 2017, TESARO initiated a registration program for an AnaptysBio-generated anti-PD-1 antagonist antibody (TSR-042) resulting in a $3.0 million milestone payment being earned. We expect to recognize as revenue and receive this milestone payment during the second quarter of 2017.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	The accompanying unaudited consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and note disclosures normally included in annual financial statements prepared in accordance with U.S. generally accepted accounting principles (“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 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 months ended March 31, 2017 are not necessarily indicative of the results that may be expected for the year ending December 31, 2017. The financial statements should be read in conjunction with our audited financial statements for the year ended December 31, 2016, included in our Annual Form 10-K.
Basis of Consolidation	The accompanying consolidated financial statements include us and our wholly-owned Australian subsidiary, which was established in March 2015. All intercompany accounts and transactions have been eliminated in consolidation. We operate in one reportable segment in the United States of America 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.
Short Term and Long Term Investments	All investments have been classified as “available-for-sale” and are carried at fair value as determined based upon quoted market prices or pricing models for similar securities at period end. Investments with contractual maturities less than 12 months at the balance sheet date are considered short-term investments. Those investments with contractual maturities greater than 12 months at the balance sheet date are considered long-term investments. Unrealized gains and losses, deemed temporary in nature, are reported as a component of accumulated other comprehensive income (loss), net of tax. A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the security. Premiums (discounts) are amortized (accreted) over the life of the related security as an adjustment to yield using the straight-line interest method. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold.
Concentration of Credit Risk	Financial instruments that potentially subject us to a concentration of credit risk consist of cash and cash equivalents and certain investments in money market funds, agency securities, commercial paper and U.S. treasury securities. Bank deposits are diversified between three financial institutions and these deposits may exceed insured limits. We are exposed to credit risk in the event of default by the financial institutions holding our cash and cash equivalents and issuers of investments that are recorded on our consolidated balance sheets. We mitigate our risk by investing in high-grade instruments and limiting the concentration in any one issuer, which limits our exposure.
Comprehensive Loss	Comprehensive loss represents all changes in stockholders’ equity (deficit) except those resulting from distributions to stockholders. Our unrealized losses on investments represent the only component of other comprehensive loss that is excluded from the reported net loss.
Net Income (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 all periods presented, there is no difference in the number of shares used to calculate basic and diluted net loss per share.
Recent Accounting Pronouncements	Accounting Pronouncements Recently Adopted In March 2016, the FASB issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. Under the new guidance, additional paid-in capital pools will be eliminated and entities will be required to recognize the income tax effects of share-based awards in the income statement when share-based awards vest or are settled. ASU 2016-09 also changes the classification of excess tax benefits on the statement of cash flows. It also will allow an employer to repurchase more of an employee's shares than it can currently for tax withholding purposes without triggering liability accounting and to make a policy election to either account for forfeitures as they occur or to continue the current practice of estimating forfeitures at the time of grant. ASU 2016-09 became effective for annual reporting periods beginning January 1, 2017, including interim periods thereafter. Upon adoption of this standard in January 2017, we recognized a cumulative increase of $41,000 to our accumulated deficit as a result of a change in accounting policy, due to our transition from calculating an estimated forfeiture rate at grant date to recording actual forfeitures as they occur. We did not record any other adjustments upon adoption of this standard. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, which requires companies to include cash and cash equivalents that have restrictions on withdrawal or use in total cash and cash equivalents on the statement of cash flows. ASU 2016-18 becomes effective for annual reporting periods beginning January 1, 2018, including interim periods thereafter; early adoption is permitted, including adoption in an interim period. Upon early adoption of this standard in January 2017, we adjusted our consolidated statement of cash flows to include $60,000 in restricted cash in the beginning and ending cash balance. We did not record any other adjustments upon adoption of this standard. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“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 becomes effective for our annual reporting period beginning January 1, 2018, including interim periods within that reporting period; adoption is permitted as early as January 1, 2017. Entities have the option of using either a full retrospective or a modified retrospective approach for the adoption of the new standard. We will transition this standard using the modified retrospective approach for our annual reporting period beginning January 1, 2018. While we are continuing to assess all potential impacts of the standard, we currently believe the most significant impact relates to our accounting for variable consideration including revenues related to contingent “milestone” based payments. 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, given the nature of potential milestones owed to us, and the inherent risk involved in developing drugs, we believe that the majority of potential milestones will not be recognizable as of the standard adoption date. 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 becomes effective for our annual reporting period beginning January 1, 2018, including interim periods within that reporting period; early adoption is permitted. We are currently assessing the impact that this standard will have on our consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires that lessees recognize a right-of-use asset and a related lease liability arising from leases on the balance sheet. ASU 2016-02 becomes effective for our annual reporting period beginning January 1, 2019, including interim periods thereafter; early adoption is permitted. We are currently reviewing all contracts outstanding and are assessing the impact that this standard will have on our consolidated financial statements.

- Definition

Disclosure of accounting policy for investments in debt and equity securities that are classified as available-for-sale. This policy also may describe the entity's accounting treatment for transfers between investment categories, how the entity determines whether impairments of available-for-sale securities are other than temporary, and how the fair values of such securities are determined.

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-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2017

Accounting Policies [Abstract]

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



	Three Months Ended March 31,
(in thousands)	2017	2016
Convertible preferred stock	—	11,521
Options to purchase common stock	1,995	2,027
Warrants to purchase preferred stock	—	294
Warrants to purchase common stock	332	117
Total	2,327	13,959

Balance Sheet Accounts and Supplemental Disclosures (Tables)

3 Months Ended

Mar. 31, 2017

Balance Sheet Related Disclosures [Abstract]

Property and Equipment

Property and equipment consist of the following:



(in thousands)	March 31, 2017			December 31, 2016
Laboratory equipment	$	3,460		$	3,383
Office furniture and equipment	595			535
Leasehold improvements	351			351
	4,406			4,269
Less: accumulated depreciation and amortization	(3,837		)	(3,798		)
Total property and equipment, net	$	569		$	471

Schedule of Accrued Expenses

Accrued expenses consist of the following:



(in thousands)	March 31, 2017		December 31, 2016
Accrued compensation and related expenses	$	659	$	973
Accrued professional fees	137		296
Accrued research and contract manufacturing expenses	3,423		2,084
Other	111		76
Total accrued expenses	$	4,330	$	3,429

Fair Value Measurements and Available for Sale Investments (Tables)

3 Months Ended

Mar. 31, 2017

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 March 31, 2017
Money market funds⁽¹⁾	$	83,309	$	83,309	$	—	$	—
Mutual funds⁽¹⁾	11,822		11,822		—		—
U.S. treasury securities⁽²⁾	4,982		4,982		—		—
Agency securities⁽²⁾	10,411		—		10,411		—
Commercial paper⁽³⁾	13,286		—		13,286		—
At December 31, 2016
Money market funds⁽¹⁾	$	31,955	$	31,955	$	—	$	—
Mutual funds⁽¹⁾	17,620		17,620		—		—
Preferred stock warrant liabilities	3,241		—		—		3,241


⁽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.


⁽³⁾	Included in cash and cash equivalents, 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			December 31, 2016
Fair value of preferred stock	$	16.95		$	12.67
Exercise price	$	4.55		$	4.55
Risk-free interest rate	1.4		%	1.5		%
Volatility	88.8		%	88.6		%
Dividend Yield	—		%	—		%
Contractual term (in years)	3.8			3.8
Weighted-average measurement date fair value per share	$	13.71		$	9.65

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):



	Three Months Ended March 31,
(in thousands)	2017			2016
Preferred Stock Warrant Liabilities:
Beginning balance	$	(3,241	)	$	(1,549	)
Net gains (losses) included in other expense	(1,366		)	379
Reclassification of warrant liabilities to equity	4,607			—
Ending balance	$	—		$	(1,170	)

Fair Value of Other Financial Instruments

The fair value of our financial instruments estimated as of March 31, 2017 and December 31, 2016 are presented below:



	March 31, 2017				December 31, 2016
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Notes payable	$	13,959	$	15,527	$	13,809	$	15,531

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 March 31, 2017 are as follows:



(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Total Fair Value
Agency securities⁽¹⁾	$	10,416	$	1	$	(6	)	$	10,411
Commercial paper⁽²⁾	13,288		1		(3		)	13,286
US treasury securities⁽³⁾	4,988		—		(6		)	4,982
Total available-for-sale investments	$	28,692	$	2	$	(15	)	$	28,679


⁽¹⁾	Agency securities have a maturity date of between one to two years as of March 31, 2017.


⁽²⁾	Of our outstanding Commercial paper, $8.4 million have maturity dates of less than one year and $4.9 million have maturity dates of between one to two years as of March 31, 2017.


⁽³⁾	Treasury securities have a maturity date of between one to two years as of March 31, 2017.

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2017

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 March 31, 2017 are as follows:



Issued and Outstanding:
Stock options	2,722,883
Warrants for shares of common stock	198,009
Shares reserved for future award grants	1,204,923
Total	4,125,815

Equity Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2017

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 three months ended March 31, 2017 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, 2017	1,879,428		$	4.34
Granted	934,141		$	22.13
Exercises	(76,863	)	$	4.63
Forfeitures and cancellations	(13,823	)	$	7.15
Outstanding at March 31, 2017	2,722,883		$	10.42	8.15	$	47,184.0

Summary of Weighted Average Assumptions in Stock Option Valuations



	Three Months Ended March 31, 2017
Risk-free interest rate	1.96		%
Expected volatility	77.64		%
Expected dividend yield	—		%
Expected term (in years)	6.18
Weighted average grant date fair value per share	$	15.15

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 March 31,
(in thousands)	2017		2016
Research and development	$	300	$	109
General and administrative	566		213
Total	$	866	$	322

Description of the Business (Details) $ / shares in Units, $ in Thousands			3 Months Ended
	Jan. 31, 2017 USD ($) $ / shares shares	Jan. 13, 2017	Mar. 31, 2017 USD ($) shares	Mar. 31, 2016 USD ($)	Jan. 30, 2017 shares	Dec. 31, 2016 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated Deficit \| $			$ 66,399			$ 54,923
Class of Warrant or Right [Line Items]
Proceeds from initial public offering, net of underwriters fees \| $			$ 80,213	$ 0
Number of shares called by warrants (in shares)			198,009
Reverse stock split, conversion ratio		0.1429
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 initial public offering (in shares)	5,750,000
Initial public offering, share price (in dollars per share) \| $ / shares	$ 15.00
Convertible preferred stock, converted to common stock (in shares)	11,520,698

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) bank segment	Jan. 01, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Accounting Policies [Abstract]
Number of reportable segments \| segment	1
Number of banks utilized for diversification of funds (in banks) \| bank	3
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 96,814		$ 51,292	$ 49,378	$ 51,744
Accounting Standards Update 2016-18 \| New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents		$ 60	$ 60	$ 60	$ 60
Retained Earnings \| Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative decrease in accumulated deficit as a result of a change in accounting policy		$ 41

Summary of Significant Accounting Policies - Summary of Potentially Dilutive Securities (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share (in shares)	2,327	13,959
Convertible Preferred 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	11,521
Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from computation of net loss per share (in shares)	1,995	2,027
Warrants \| Preferred 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	294
Warrants \| 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)	332	117

Balance Sheet Accounts and Supplemental Disclosures - Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,406	$ 4,269
Less: accumulated depreciation and amortization	(3,837)	(3,798)
Total property and equipment, net	569	471
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,460	3,383
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	595	535
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 351	$ 351

Balance Sheet Accounts and Supplemental Disclosures - Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Balance Sheet Related Disclosures [Abstract]
Accrued compensation and related expenses	$ 659	$ 973
Accrued professional fees	137	296
Accrued research and contract manufacturing expenses	3,423	2,084
Other	111	76
Total accrued expenses	$ 4,330	$ 3,429

Collaborative Research and Development Agreements (Details)	1 Months Ended				3 Months Ended		12 Months Ended
	Feb. 29, 2016 USD ($)	Jan. 31, 2016 USD ($)	Nov. 30, 2014 USD ($) target	Mar. 31, 2014 USD ($) target	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) milestone	Dec. 31, 2011 USD ($) $ / target
Deferred Revenue Arrangement [Line Items]
Collaboration revenue					$ 0	$ 4,866,000
Collaborative Research And Development Agreement \| TESARO
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
Milestone method, revenue recognized						3,000,000
Collaboration revenue					0	4,900,000
Revenue recognized, funding for research and development services						1,200,000
Amortization of upfront fee						700,000
Collaborative Research And Development Agreement \| TESARO \| AnaptysBio-generated Anti-PD-1 Antagonist Antibody And AnaptysBio-generated Anti-TIM-3 Antagonist Antibody
Deferred Revenue Arrangement [Line Items]
Number of milestones achieved during period \| milestone							2
Milestones achieved during period, amount							$ 1,000,000
Milestone method, revenue recognized						77,000
Collaborative Research And Development Agreement \| Celgene Corporation
Deferred Revenue Arrangement [Line Items]
Upfront license fee received								$ 6,000,000
Collaboration revenue					$ 0	0
Maximum milestone payments per target \| $ / target								53,000,000
Clearance Of IND From FDA \| TESARO
Deferred Revenue Arrangement [Line Items]
Milestone method, revenue recognized						$ 2,900,000
Milestone payment earned		$ 4,000,000
Milestone payment received	$ 4,000,000

Notes Payable (Details)			1 Months Ended
Notes Payable (Details)	Dec. 30, 2016 USD ($) $ / shares shares	Dec. 24, 2014 USD ($) installment program $ / shares shares	Dec. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Mar. 31, 2017 USD ($) payment shares
Debt Instrument [Line Items]
Number of shares called by warrants (in shares) \| shares					198,009
Notes payable, current portion			$ 0		$ 1,250,000
Warrants \| Term A Loan Warrants
Debt Instrument [Line Items]
Preferred stock warrant liabilities		$ 100,000
Expected stock price volatility (as a percent)		70.20%
Contractual term (in years)		10 years
Risk-free interest rate (as a percent)		1.97%
Warrants \| Term B And C Loans Warrants
Debt Instrument [Line Items]
Preferred stock warrant liabilities	$ 900,000
Expected stock price volatility (as a percent)	79.20%
Contractual term (in years)	10 years
Risk-free interest rate (as a percent)	2.45%
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
Effective interest rate (as a percent)					11.82%
Notes payable					$ 14,000,000
Debt instrument discounts					1,000,000
Notes payable, current portion					1,300,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2018					6,900,000
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%
Cost incurred to issue debt		$ 85,000
Final payment fee due at the earlier of prepayment or maturity date		300,000
Notes Payable to Banks \| Term B and Term C Loans
Debt Instrument [Line Items]
Aggregate borrowing capacity				$ 10,000,000
Fixed interest rate (as a percent)				6.95%
Number of interest only payments for term loans (in payments) \| payment					10
Number of principal and interest payments (in payments) \| payment					24
Notes Payable to Banks \| Term B and Term C Loans \| 3-Month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)				6.72%
Notes Payable to Banks \| Term B Loans
Debt Instrument [Line Items]
Debt instrument, maximum borrowing capacity		$ 5,000,000
Fixed interest rate (as a percent)		6.97%	7.30%
Number of development programs achieving specified targets for availability of funds (in programs) \| program		2
Effective interest rate (as a percent)					7.43%
Notes Payable to Banks \| Term B Loans \| 3-Month LIBOR
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]
Debt instrument, maximum borrowing capacity		$ 5,000,000
Fixed interest rate (as a percent)		6.97%	7.30%
Number of development programs achieving specified targets for availability of funds (in programs) \| program		2
Effective interest rate (as a percent)					7.43%
Notes Payable to Banks \| Term C Loans \| 3-Month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)			6.37%

Fair Value Measurements and Available for Sale Investments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	$ 28,679
Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	10,411
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	13,286
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liabilities		$ 3,241
Fair Value, Measurements, Recurring \| U.S. treasury security
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	4,982
Fair Value, Measurements, Recurring \| Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	10,411
Fair Value, Measurements, Recurring \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	13,286
Fair Value, Measurements, Recurring \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	83,309	31,955
Fair Value, Measurements, Recurring \| Mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments at fair value	11,822	17,620
Fair Value, Measurements, Recurring \| Quoted Market Prices for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liabilities		0
Fair Value, Measurements, Recurring \| Quoted Market Prices for Identical Assets (Level 1) \| U.S. treasury security
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	4,982
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]
Total Fair Value	0
Fair Value, Measurements, Recurring \| Quoted Market Prices for Identical Assets (Level 1) \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	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	83,309	31,955
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	11,822	17,620
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liabilities		0
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| U.S. treasury security
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	0
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]
Total Fair Value	10,411
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	13,286
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)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liabilities		3,241
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| U.S. treasury security
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	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]
Total Fair Value	0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Fair Value	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

Fair Value Measurements and Available for Sale Investments - Fair Value Assumptions (Details) - Derivative Financial Instruments, Liabilities - Fair Value, Measurements, Recurring - Series C Preferred Stock - $ / shares		12 Months Ended
	Jan. 31, 2017	Dec. 31, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value of preferred stock (in dollars per share)	$ 16.95	$ 12.67
Exercise price (in dollars per share)	$ 4.55	$ 4.55
Risk-free interest rate (as a percent)	1.40%	1.50%
Volatility (as a percent)	88.80%	88.60%
Dividend Yield (as a percent)	0.00%	0.00%
Contractual term (in years)	3 years 9 months	3 years 9 months 30 days
Weighted-average measurement date fair value per share (in dollars per share)	$ 13.71	$ 9.65

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 - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (3,241)	$ (1,549)
Unrealized net gain (loss) included in other expense, net	(1,366)	379
Reclassification of warrant liabilities to equity	4,607	0
Ending balance	$ 0	$ (1,170)

Fair Value Measurements and Available for Sale Investments - Fair Value of Other Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	$ 13,959	$ 13,809
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	$ 15,527	$ 15,531

Fair Value Measurements and Available for Sale Investments - Available-for-sale Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 28,692
Gross Unrealized Gains	2
Gross Unrealized Losses	(15)
Total Fair Value	28,679
Long-term investments	20,327	$ 0
Agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,416
Gross Unrealized Gains	1
Gross Unrealized Losses	(6)
Total Fair Value	$ 10,411
Agency securities \| Minimum
Schedule of Available-for-sale Securities [Line Items]
Investments outstanding, maturity date range (in years)	1 year
Agency securities \| Maximum
Schedule of Available-for-sale Securities [Line Items]
Investments outstanding, maturity date range (in years)	2 years
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 13,288
Gross Unrealized Gains	1
Gross Unrealized Losses	(3)
Total Fair Value	13,286
Commercial paper having maturities dates of less than one year	8,400
Long-term investments	$ 4,900
Commercial paper \| Minimum
Schedule of Available-for-sale Securities [Line Items]
Investments outstanding, maturity date range (in years)	1 year
Commercial paper \| Maximum
Schedule of Available-for-sale Securities [Line Items]
Investments outstanding, maturity date range (in years)	2 years
US treasury securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 4,988
Gross Unrealized Gains	0
Gross Unrealized Losses	(6)
Total Fair Value	$ 4,982
US treasury securities \| Minimum
Schedule of Available-for-sale Securities [Line Items]
Investments outstanding, maturity date range (in years)	1 year
US treasury securities \| Maximum
Schedule of Available-for-sale Securities [Line Items]
Investments outstanding, maturity date range (in years)	2 years

Stockholders' Equity - Additional Information (Details) - $ / shares	27 Months Ended
	Mar. 31, 2017	Jan. 31, 2017	Jan. 13, 2017	Dec. 31, 2016
Equity [Abstract]
Common stock, shares authorized (in shares)	500,000,000	500,000,000	60,000,000	17,214,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000		11,520,698	0
Preferred stock, par value (in dollars per share)	$ 0.001		$ 0.001	$ 0.001
Common stock, shares issued (in shares)	20,249,295			2,651,000
Common stock, shares outstanding (in shares)	20,249,295			2,651,000
Common Stock
Class of Stock [Line Items]
Warrants exercised, number of shares represented (as shares)	296,669
Warrants exercised, number of shares represented, cashless exercise (as shares)	179,047
Shares issued as a result of warrants exercised (in shares)	250,448

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Details) - shares	Mar. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Stock options outstanding (in shares)	2,722,883	1,879,428
Warrant for shares of common stock (in shares)	198,009
Shares reserved for future award grants (in shares)	1,204,923
Common stock, shares reserved for issuance (in shares)	4,125,815

Equity Incentive Plans - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended
	Jan. 26, 2017	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares reserved for issuance (in shares)		4,125,815
Stock options outstanding (in shares)		2,722,883		1,879,428
Shares reserved for future award grants (in shares)		1,204,923
Proceeds from issuance of common stock, upon the exercise of stock options		$ 355	$ 9
Granted (in shares)		934,141	0
Unrecognized compensation cost		$ 16,700
Options \| Director
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
Employee and Nonemployee Stock Options
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)		3 years 1 month
Equity Incentive Plan, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares reserved for issuance (in shares)	1,955,506
Annual increase in number of shares available for issuance (as a percent)	4.00%
Stock options outstanding (in shares)		2,722,883
Shares reserved for future award grants (in shares)		1,204,923
Equity Incentive Plan, 2006
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares reserved for issuance (in shares)	308,343
Employee Stock Purchase Plan, 2017 \| Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares reserved for issuance (in shares)		218,000
Annual increase in number of shares available for issuance (as a percent)	1.00%

Equity Incentive Plans - Option Activity (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Stock options outstanding, beginning balance (in shares)	1,879,428
Granted (in shares)	934,141	0
Exercises (in shares)	(76,863)
Forfeitures and cancellations (in shares)	(13,823)
Stock options outstanding, ending balance (in shares)	2,722,883
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Stock options outstanding, beginning balance (in dollars per share)	$ 4.34
Granted (in dollars per share)	22.13
Exercises (in dollars per share)	4.63
Forfeitures and cancellations (in dollars per share)	7.15
Stock options outstanding, ending balance (in dollars per share)	$ 10.42
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual term, options outstanding (in years)	8 years 1 month 25 days
Aggregate intrinsic value, options outstanding	$ 47,184,000

Equity Incentive Plans - Option Fair Value Assumptions (Details) - Options	3 Months Ended
	Mar. 31, 2017 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (as a percent)	1.96%
Expected volatility (as a percent)	77.64%
Expected dividend yield (as a percent)	0.00%
Expected term (in years)	6 years 2 months 5 days
Weighted average grant date fair value per share (in dollars per share)	$ 15.15

Equity Incentive Plans - Allocation of Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 866	$ 322
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	300	109
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 566	$ 213

Australia Research and Development Tax Incentive (Details) - Australian Taxation Office - Subsidiaries - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Refundable tax incentive for qualified research and development activities (as a percent)	43.50%		45.00%
Research and development	$ 600,000	$ 0

Subsequent Events (Details)	1 Months Ended
Subsequent Events (Details)	Apr. 30, 2017 USD ($)
Collaborative Research And Development Agreement \| TESARO \| Subsequent Event
Subsequent Event [Line Items]
Milestone payment earned	$ 3,000,000