Aimmune Therapeutics (AIMT) 10-K 20 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 15, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	AIMT
Entity Registrant Name	AIMMUNE THERAPEUTICS, INC.
Entity Central Index Key	1,631,650
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		51,525,596
Entity Public Float			$ 736,657,604

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 73,487	$ 124,010
Short-term investments	108,943	124,921
Prepaid expenses and other current assets	6,681	2,749
Total current assets	189,111	251,680
Long-term investments		33,602
Property and equipment, net	17,205	10,391
Prepaid expenses and other assets	618	3,116
Total assets	206,934	298,789
Current liabilities:
Accounts payable	5,095	1,427
Accrued liabilities	21,478	9,921
Other current liabilities	26	102
Total current liabilities	26,599	11,450
Other liabilities	2,530	1,367
Total liabilities	29,129	12,817
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, par value $0.0001 per share - 10,000 shares authorized at December 31, 2017 and 2016; 0 shares issued and outstanding at December 31, 2017 and 2016
Common stock, par value $0.0001 per share—290,000 shares authorized as of December 31, 2017 and 2016; 51,091 and 50,204 shares issued and outstanding as of December 31, 2017 and 2016, respectively (including 47 and 200 shares subject to repurchase, legally issued and outstanding as of December 31, 2017 and 2016, respectively)	5	5
Additional paid-in capital	443,390	420,151
Accumulated other comprehensive loss	(108)	(27)
Accumulated deficit	(265,482)	(134,157)
Total stockholders’ equity	177,805	285,972
Total liabilities and stockholders’ equity	$ 206,934	$ 298,789

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	290,000,000	290,000,000
Common stock, shares issued	51,091,000	50,204,000
Common stock, shares outstanding	51,091,000	50,204,000
Common Stock Subject to Repurchase
Common stock, shares issued	47,000	200,000
Common stock, shares outstanding	47,000	200,000

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses
Research and development	$ 89,325	$ 54,642	$ 19,816
General and administrative	43,949	26,885	16,181
Total operating expenses	133,274	81,527	35,997
Loss from operations	(133,274)	(81,527)	(35,997)
Interest income, net	2,005	703	181
Loss before provision for income taxes	(131,269)	(80,824)	(35,816)
Provision for income taxes	56
Net loss	(131,325)	(80,824)	(35,816)
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on investments	(81)	61	(88)
Comprehensive loss	$ (131,406)	$ (80,763)	$ (35,904)
Net loss per common share, basic and diluted	$ (2.61)	$ (1.89)	$ (1.88)
Weighted average shares used in computing net loss per share, basic and diluted	50,401	42,751	19,041

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated deficit
Beginning balance at Dec. 31, 2014	$ 671	$ 16,928			$ 1,260		$ (17,517)
Beginning balances (in shares) at Dec. 31, 2014		13,264		4,252
Issuance of convertible preferred stock	79,779		$ 79,779
Issuance of convertible preferred stock (in shares)			14,048
Issuance of common stock upon exercise of vested options	303				303
Issuance of common stock upon exercise of vested options (in shares)				1,436
Issuance common stock upon initial public offering	168,119			$ 1	168,118
Issuance common stock upon initial public offering (in shares)				11,500
Repurchase of convertible preferred stock	(12,874)	$ (12,874)
Repurchase of convertible preferred stock (in shares)		(2,261)
Conversion of preferred stock to common stock		$ (4,054)	$ (79,779)	$ 3	83,830
Conversion of preferred stock to common stock (in shares)		(11,003)	(14,048)	25,051
Stock-based compensation	6,157				6,157
Other comprehensive gain (loss)	(88)					$ (88)
Net loss	(35,816)						(35,816)
Ending balances at Dec. 31, 2015	206,251			$ 4	259,668	(88)	(53,333)
Ending balances (in shares) at Dec. 31, 2015				42,239
Issuance of common stock upon exercise of vested options	2,843				2,843
Issuance of common stock upon exercise of vested options (in shares)				413
Issuance of common stock upon securities purchase agreement	145,000			$ 1	144,999
Issuance of common stock upon securities purchase agreement (in shares)				7,552
Stock-based compensation	12,641				12,641
Other comprehensive gain (loss)	61					61
Net loss	(80,824)						(80,824)
Ending balances at Dec. 31, 2016	285,972			$ 5	420,151	(27)	(134,157)
Ending balances (in shares) at Dec. 31, 2016				50,204
Issuance of common stock upon exercise of vested options and vesting of restricted stock units	6,520				6,520
Issuance of common stock upon exercise of vested options and vesting of restricted stock units (in shares)				887
Stock-based compensation	16,719				16,719
Other comprehensive gain (loss)	(81)					(81)
Net loss	(131,325)						(131,325)
Ending balances at Dec. 31, 2017	$ 177,805			$ 5	$ 443,390	$ (108)	$ (265,482)
Ending balances (in shares) at Dec. 31, 2017				51,091

CONSOLIDATED STATEMENTS OF STO6

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - Series B Convertible Preferred Stock - USD ($)	12 Months Ended
	Dec. 31, 2015	Feb. 28, 2015
Share price (per share)	$ 5.69	$ 5.69
Stock issuance costs	$ 221,000

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (131,325)	$ (80,824)	$ (35,816)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation expense	966	534	115
Stock-based compensation expense	16,719	12,641	6,157
Investment premium amortization, net	511	919	324
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,435)	3,967	(9,698)
Accounts payable	2,315	(994)	1,072
Accrued liabilities	11,557	6,803	1,859
Other liabilities	1,087	340	297
Net cash used in operating activities	(99,605)	(56,614)	(35,690)
Cash flows from investing activities:
Purchases of property and equipment	(6,425)	(7,665)	(1,708)
Purchases of investments	(129,534)	(197,178)	(152,811)
Maturities of investments	178,521	160,947	29,250
Change in restricted cash			40
Net cash provided by (used in) investing activities	42,562	(43,896)	(125,229)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	6,520	145,000	168,119
Net cash proceeds from exercise of stock options, including early exercise		2,843	303
Net cash provided by financing activities	6,520	147,843	235,327
Net increase (decrease) in cash and cash equivalents	(50,523)	47,333	74,408
Cash and cash equivalents at the beginning of the period	124,010	76,677	2,269
Cash and cash equivalents at the end of the period	73,487	124,010	76,677
Supplemental schedule of non-cash investing and financing activities:
Purchases of property and equipment reported in accounts payable	1,355	$ 558
Capital expenditures and interest funded through long term lease obligation			710
Supplemental cash flow disclosures:
Cash paid for taxes	$ 39
Series B Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from issuance, net of issuance costs			79,779
Series A Convertible Preferred Stock
Cash flows from financing activities:
Repurchase of preferred stock			(12,874)
Initial Public Offering
Supplemental schedule of non-cash investing and financing activities:
Conversion of convertible preferred stock to common stock at closing of initial public offering			$ 83,833

Formation and Business of the C

Formation and Business of the Company	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Formation and Business of the Company	1. Formation and Business of the Company Aimmune Therapeutics, Inc., or the Company, is a clinical-stage biopharmaceutical company advancing a new therapeutic approach, including the development of proprietary product candidates, for the treatment of peanut and other food allergies. Our therapeutic approach, which we refer to as Characterized Oral Desensitization Immunotherapy, or CODIT TM Since inception, we have incurred net losses and negative cash flows from operations. During the year ended December 31, 2017, we incurred a net loss of $131.3 million and used $99.6 million of cash in operations. As of December 31, 2017, we had an accumulated deficit of $265.5 million and we do not expect to experience positive cash flows in the near future. As of December 31, 2017, we had cash, cash equivalents and investments of $182.4 million. We believe that our existing capital resources will be sufficient to fund our planned operations for the next 12 months and through regulatory submission of a Biologics License Application, or BLA, for AR101, our lead CODIT TM Private Placement On November 23, 2016, we completed the issuance and sale of 7,522,084 shares of our common stock for an aggregate cash purchase price of $145.0 million, or the Equity Investment, pursuant to a Securities Purchase Agreement, or the Purchase Agreement, dated November 2, 2016, by and between us and Nestle Health Science US Holdings, Inc., a Delaware corporation, or Nestle Health Science. In connection with the closing of the Equity Investment, we and Nestle Health Science entered into a Standstill Agreement, or the Standstill Agreement, and a Registration Rights Agreement, or the Registration Rights Agreement. See Note 6, “Stockholders’ Equity.” Initial Public Offering On August 5, 2015, our registration statement on Form S-1 (File No. 333-205501) relating to the IPO of our common stock became effective. The IPO closed on August 11, 2015 at which time we issued 11,499,999 shares of our common stock at a price of $16.00 per share, which included 1,499,999 shares sold pursuant to the exercise in full of the underwriters’ option to purchase additional shares. We received proceeds of approximately $168.1 million, net of underwriting discounts and commissions, and offering expenses. In addition, upon our IPO, all outstanding shares of convertible preferred stock converted by their terms into approximately 25.1 million shares of common stock. As of December 31, 2017, we had 51,090,813 shares of common stock outstanding. See Note 6, “Stockholders’ Equity.” Stock Split On July 30, 2015, we effected a 1-for-1.317 stock split of our common stock and convertible preferred stock. The par value of the authorized stock was not adjusted as a result of the stock split. In addition, we increased the number of authorized shares of common stock to 55,051,264 and the number of authorized shares of preferred stock to 25,051,264. All issued and outstanding common stock, convertible preferred stock, stock options and per share amounts contained in the accompanying consolidated financial statements and accompanying notes have been retroactively adjusted to give effect to the stock split for all periods presented. In conjunction with the our IPO, we filed our amended and restated certificate of incorporation that authorized 290,000,000 shares of common stock, $0.0001 par value per share, and 10,000,000 shares of preferred stock, $0.0001 par value per share.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Preparation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States, or U.S. GAAP, and include the accounts of our wholly-owned subsidiaries. All significant intercompany transactions have been eliminated. We operate in one reportable segment in the United States. Foreign Currency Translation Our functional currency and the functional currency of all of our subsidiaries is the United States dollar. Accordingly, monetary assets and liabilities in the non-functional currency of these subsidiaries are remeasured using exchange rates in effect at the end of the period. Costs in local currency are remeasured using average exchange rates for the period, except for costs related to those balance sheet items that are remeasured using historical exchange rates. The resulting remeasurement gains and losses are included in the consolidated statements of operations and comprehensive loss as incurred and have not been material for all periods presented. Use of Estimates The preparation of the accompanying consolidated financial statements in accordance with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of costs and expenses during the reporting period. 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. Cash and Cash Equivalents We consider all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents, which are carried at estimated fair value, consist primarily of money market funds and certain available-for-sale investments with maturities of three months or less. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. We have one operating segment. 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, corporate securities, U.S. government securities and commercial paper. Bank deposits are primarily held by a single financial institution and these deposits may exceed insured limits. We are exposed to credit risk in the event of default by the financial institution 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. Investments Our investments consist of available-for-sale securities. Investments with original maturities of greater than 90 days but less than one (1) year are classified as short-term on the consolidated balance sheets. Investments with original maturities greater than one (1) year are classified as long-term on the consolidated balance sheets. Our investments in available-for-sale securities are reported at estimated fair value. Available-for-sale securities consist primarily of agency securities, corporate securities, U.S. government securities and commercial paper. Unrealized gains and losses related to changes in the fair value of securities are recognized in accumulated other comprehensive loss, net of tax, on our consolidated balance sheets. Changes in the fair value of available-for-sale securities impact the consolidated statements of operations and comprehensive loss only when such securities are sold or an other-than-temporary impairment is recognized. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. We regularly review our investment portfolio to determine if any security is other-than-temporarily impaired, which would require us to record an impairment charge in the period any such determination is made. We consider factors such as the duration, severity and the reason for the decline in value, the financial condition of the issuer and any changes thereto, the potential recovery period and our intent to sell. For debt securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis, and (ii) the amortized cost basis cannot be recovered as a result of credit losses. Our assessment on whether a security is other-than-temporarily impaired could change in the future due to new developments or changes in assumptions related to any particular security. Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets. Maintenance and repairs are charged to the consolidated statements of operations and comprehensive loss as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss, if any, is reflected in the consolidated statements of operations and comprehensive loss. The useful lives of property and equipment are as follows: Furniture and office equipment 4 years Computer equipment 3 years Buildings 25 years Fixtures 10 years Leasehold improvements Shorter of remaining lease terms or useful life Impairment of Long-Lived Assets We evaluate our long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows expected to result from the use of the asset and its eventual disposition. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired assets. We have not recorded impairment of any long-lived assets in the periods presented. Leases Leases related to our corporate headquarters are classified as operating leases. Rent expense is recognized on a straight-line basis over the terms of the leases and, accordingly, we record the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Incentives granted under facilities leases are deferred and recognized as adjustments to rental expense on a straight-line basis over the term of the lease. In June 2015, we signed a lease for a manufacturing facility in Clearwater, Florida. We were considered the deemed owner for accounting purposes. See Note 5, “Commitments and Contingencies,” for further details. Research and Development We expense research and development costs as incurred. We record accrued liabilities for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of pre-clinical studies and clinical trials and contract manufacturing activities. These costs are a significant component of our research and development expenses. We accrue for these costs based on factors such as estimates of the work completed and in accordance with agreements established with our third-party service providers under the service agreements. We make significant judgments and estimates in determining the accrued liabilities balance in each reporting period. As actual costs become known, we adjust our accrued liabilities. We have not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled and the rate of patient enrollments may vary from our estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to our accruals could materially affect our results of operations. Stock-Based Compensation Stock-based awards issued to employees, including stock options, are measured at fair value on the grant date using the Black--Scholes option-pricing model for stock options and the market price of our ordinary shares on that date for restricted stock units (“RSUs”). The fair value stock-based awards is Income Taxes We use the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of reported assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. We must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to our lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. Tax benefits from uncertain tax positions are recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on technical merits. The amount recognized is measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon effective settlement. Comprehensive Income or Loss Comprehensive income or loss is defined as the change in equity during a period from transactions and other events, excluding changes resulting from investments from owners and distributions to owners. Other comprehensive loss includes net loss and unrealized gains and losses on available-for-sale investments. Net Loss per Share The following common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive: Year Ended December 31, 2017 2016 2015 Series A convertible preferred stock — — — Stock options 6,629,111 5,429,267 4,814,892 Restricted stock units 16,638 17,000 — Offering Costs Offering costs represent underwriting, legal, accounting and other direct costs related to our IPO. These costs were deferred until completion of the IPO, at which time they were reclassified to additional paid-in capital as a reduction of the proceeds. Fair Value Measurements We define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Our valuation techniques are based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect our market assumptions. We classify these inputs into the following hierarchy: Level 1 —Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; 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 significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Financial instruments include cash equivalents, investments, accounts payable, and accrued liabilities. Our cash equivalents and investments are carried at estimated fair value and remeasured on a recurring basis. The carrying value of accounts payable and accrued liabilities approximate their estimated fair value due to the relatively short-term nature of these instruments. Our valuation techniques used to measure the fair value of money market funds were derived from quoted prices in active markets for identical assets. The valuation techniques used to measure the fair value of investments, all of which have counterparties with high credit ratings, were valued based on quoted market prices or model-driven valuations using significant inputs derived from or corroborated by observable market data. In accordance with fair value accounting requirements, companies may choose to measure eligible financial instruments and certain other items at fair value. We have not elected the fair value option for any eligible financial instruments. Recently Adopted Accounting Pronouncements In March 2016, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2016-09, Compensation—Stock Compensation (Topic 718) Improvements to Employee Share-Based Payment Accounting , which simplifies several aspects of accounting for share-based payment transactions including the income tax consequences, classification of awards as either equity or liabilities, classification on the statement of cash flows and accounting for forfeitures. Upon our adoption of the new standard for fiscal year 2017, all excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in the income statement. The tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. We recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. We applied the modified retrospective approach upon adoption, and prior periods have not been adjusted. As a result, we have established a net operating loss deferred tax asset of $1.2 million to account for prior period excess tax benefits through retained earnings; however, an offsetting valuation allowance of $1.2 million has also been established through retained earnings because it is not more likely than not that the deferred asset will be realized due to historical and expected future losses, such that there is no impact on our consolidated financial statements. Additionally, as allowed by the standard, we elected to continue to estimate potential forfeitures. Recently Issued Accounting Pronouncements Not Yet Adopted In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting In November 2016, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2016-18, Statement of Cash Flows – Restricted Cash (Topic 230) In October 2016, the FASB, issued ASU, 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers Other Than Inventory In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In February 2016, the FASB, issued ASU, No. 2016-02, Leases (Topic 842)

Available-for-Sale Securities a

Available-for-Sale Securities and Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Available-for-Sale Securities and Fair Value Measurements	3. Available-for-Sale Securities and Fair Value Measurements The following table sets forth our financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Cash and cash equivalents: Cash and money market funds $ 39,072 $ — $ — $ 39,072 Corporate securities — 999 — 999 Commercial paper — 33,416 — 33,416 Total cash and cash equivalents $ 39,072 $ 34,415 $ — $ 73,487 Investments: Agency securities — 12,718 — 12,718 Corporate securities — 28,345 — 28,345 Commercial paper — 21,432 — 21,432 US government securities — 46,448 — 46,448 Total investments $ — $ 108,943 $ — $ 108,943 December 31, 2016 Level 1 Level 2 Level 3 Total Cash and cash equivalents: Cash and money market funds $ 107,977 $ — $ — $ 107,977 Commercial paper — 16,033 — 16,033 Total cash and cash equivalents $ 107,977 $ 16,033 $ — $ 124,010 Investments: Agency securities $ — $ 45,571 $ — $ 45,571 Corporate securities — 22,031 — 22,031 Commercial paper — 8,669 — 8,669 US government securities — 82,252 — 82,252 Total investments $ — $ 158,523 $ — $ 158,523 Our valuation techniques used to measure the fair value of money market funds were derived from quoted prices in active markets for identical assets. The valuation techniques used to measure the fair value of investments, all of which have counterparties with high credit ratings, were valued based on quoted market prices or model-driven valuations using significant inputs derived from or corroborated by observable market data. Investments are carried at fair value. During the years ended December 31, 2017 and 2016, there were no transfers between Level 1 and Level 2 of the fair value hierarchy. Available-for-sale 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 and investments, as of December 31, 2017 and December 31, 2016 are as are as follows (in thousands): December 31, 2017 Amortized Cost Gross unrealized gains Gross unrealized losses Total fair value Agency securities $ 12,729 $ — $ (11 ) $ 12,718 Corporate securities 29,369 1 (26 ) 29,344 Commercial paper 54,848 — — 54,848 US government securities 46,520 — (72 ) 46,448 Total available-for-sale investments $ 143,466 $ 1 $ (109 ) $ 143,358 December 31, 2016 Amortized Cost Gross unrealized gains Gross unrealized losses Total fair value Agency securities $ 45,591 $ 5 $ (25 ) $ 45,571 Corporate securities 22,050 2 (21 ) 22,031 Commercial paper 24,702 — — 24,702 US government securities 82,240 15 (3 ) 82,252 Total available-for-sale investments $ 174,583 $ 22 $ (49 ) $ 174,556 At December 31, 2017, all of the available-for-sale securities have contractual maturities within one year. We periodically review our available-for-sale investments for other-than-temporary impairment loss. We consider factors such as the duration, severity and the reason for the decline in value, the potential recovery period and our intent to sell. For debt securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis, and (ii) the amortized cost basis cannot be recovered as a result of credit losses. During the years ended December 31, 2017, 2016, and 2015 we did not recognize any other-than-temporary impairment losses. All marketable securities with unrealized losses have been in a loss position for less than twelve months.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	4. Balance Sheet Components Property and Equipment, Net Property and equipment, net consists of the following (in thousands): Year Ended December 31, 2017 2016 Furniture and equipment $ 1,655 $ 776 Computer equipment 1,410 850 Manufacturing equipment 830 703 Leased equipment 100 — Leasehold improvements 2,685 — Buildings 688 — Construction in progress 11,490 8,749 Property and equipment, gross 18,858 11,078 Less: accumulated depreciation (1,653 ) (687 ) Property and equipment, net $ 17,205 $ 10,391 Depreciation expense for the years ended December 31, 2017, 2016 and 2015 was $1.0 million, $0.5 million and $0.1 million, respectively. Accrued Liabilities Accrued liabilities consist of the following (in thousands): Year Ended December 31, 2017 2016 Compensation and benefits $ 6,205 $ 3,195 Research and development 12,716 5,154 Professional and consulting 2,370 967 Other 187 605 Total accrued liabilities $ 21,478 $ 9,921

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	5. Commitments and Contingencies Facility Leases In March 2015, we entered into a new lease for our corporate headquarters in Brisbane, California for 11,665 square feet of office space. In August 2015, we entered into a lease amendment, pursuant to which we leased an additional 26,355 square feet of office space. In June 2017, we entered into a second lease amendment, under which we leased an additional 14,841 square feet of office space. The term for the additional space commenced on January 1, 2018 and terminates on June 30, 2024. Additionally, the term of the existing office space has been extended so that it is coterminous with the new space. No additional security deposit was required, and we are responsible for operating expenses over base operating expenses as defined in the original lease agreement. We also lease office space in Durham, North Carolina and London, United Kingdom with lease terms that are less than twelve months. In June 2015, we signed a facility lease for a manufacturing facility for approximately 20,000 square feet of manufacturing space in Clearwater, Florida. The initial term of the lease is for 120 months. For accounting purposes, due to the nature and extent of our involvement with the construction of this manufacturing facility, we were considered to be the owner of the assets during the construction period through the lease commencement date, even though the lessor is responsible for funding and repairing components of the building shell and constructing a portion of the related building infrastructure. We capitalized $0.7 million for costs incurred by the lessor in constructing the building shell and recognized a corresponding amount included within other liabilities. Construction to this building commenced in July 2015 and as of December 31, 2017, we have incurred approximately $13.3 million of construction and equipment costs related to the building, of which $10.4 million is recorded in construction in progress. We are responsible for operating expenses including real estate taxes as defined in the manufacturing facility lease agreement. Total future aggregate minimum lease payments under our operating leases, are as follows (in thousands): Year Ended December 31, 2018 $ 2,985 2019 2,557 2020 2,645 2021 2,724 2022 2,805 and thereafter 4,611 Total $ 18,327 Rent expense under operating leases for the years ended December 31, 2017, 2016 and 2015 was $2.4 million, $1.7 million and $0.6 million, respectively. Capital Lease In July 2016, we entered into a five year capital lease agreement for certain equipment in our Florida manufacturing facility. The current portion of the capital lease obligation is included in Other Current Liabilities and the noncurrent portion is included in Other Liabilities. The following is a schedule of future minimum lease payments due under the capital lease obligation as of December 31, 2017 (in thousands): Year Ended December 31, 2018 $ 33 2019 33 2020 34 2021 35 2022 9 Total capital lease obligation 144 Less: amount representing interest (53 ) Present value of net minimum capital lease payments 91 Less: current portion (14 ) Total noncurrent capital lease obligation $ 77 Purchase Commitments We purchase standard food-grade peanut flour from Golden Peanut Company, or GPC, pursuant to a long-term exclusive commercial supply agreement, which was expanded and extended in January 2018. GPC is not allowed to sell several peanut flour products to any third party worldwide for use in OIT for the treatment or cure of peanut allergy, provided that we are in compliance with our exclusive purchase obligation and meet specified annual purchase commitments. The restated agreement remains in effect until ten years five years. 300,000 Pursuant with the restated agreement, our purchase obligation commences with the first delivery of peanut flour for commercial use, which we currently anticipate will not occur prior to 2019. Assuming that our first delivery for commercial use occurs in 2019, which is not assured, the aggregate purchase commitment under this agreement would be $8.3 million over a term of ten years. Indemnifications We indemnify each of our officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at the Company’s request in such capacity, as permitted under Delaware law and in accordance with our certificate of incorporation and bylaws. The term of the indemnification period lasts as long as an officer or a director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity. The maximum amount of potential future indemnification is unlimited; however, we currently hold directors’ and officers’ liability insurance. This insurance allows the transfer of risk associated with our exposure and may enable us to recover a portion of any future amounts paid. We believe that the fair value of these indemnification obligations is minimal. Accordingly, we have not recognized any liabilities relating to these obligations for any period. Legal We are currently not a party to any material legal proceedings. During the normal course of business, we may be a party to legal claims that may not be covered by insurance. We do not believe that any such claims would have a material impact on our consolidated financial statements.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	6. Stockholders’ Equity Convertible Preferred Stock In January and February 2015, we issued an aggregate 14,047,996 shares of Series B convertible preferred stock, $0.0001 par value, original issue price of $5.69 per share, for gross cash proceeds of $80.0 million, and in January 2015, we repurchased 2,260,706 shares of Series A convertible preferred stock from certain investors. The purchase price of the Series A convertible preferred stock was $5.69 per share, the same as the issue price of the Series B convertible stock, and was at an aggregate cost of $12.9 million. The offering costs for the issuance and sale of Series B convertible preferred stock was $221,000. All 25,051,257 shares of our then-outstanding convertible preferred stock converted into an equivalent number of shares of common stock upon the closing of our IPO on August 11, 2015. As of December 31, 2017 and 2016, we had authorized 10,000,000 shares of convertible preferred stock, and no shares of convertible preferred stock were issued and outstanding. Common Stock On November 23, 2016, we issued and sold 7,522,084 shares of our common stock, par value $0.0001 per share, for an aggregate cash purchase price of $145.0 million, pursuant to the Purchase Agreement, dated November 2, 2016, by and between us and Nestle Health Science. In connection with the closing of the Equity Investment, we and Nestle Health Science entered into a Registration Rights Agreement and a Standstill Agreement. Under the terms of the Registration Rights Agreement, upon the written request of Nestle Health Science, we shall prepare and file with the Securities and Exchange Commission, or the Commission, a registration statement covering the resale of all the shares sold to Nestle Health Science that are not then registered on an existing and effective registration statement for an offering to be made on a continuous basis pursuant Commission Rule 415. Additionally, we shall use commercially reasonable efforts to cause such registration statement filed under the Registration Rights Agreement to be declared effective under the Securities Act of 1933, as amended, within certain defined time limits and to keep such registration statement continuously effective for a period of potentially three years from the original effect date of such registration statement. Under the terms of the Standstill Agreement, Nestle Health Science is prohibited from entering into transactions with the shares purchased in the Equity Investment, as well as to enter into any transactions with any of our assets, without prior written consent of a majority of the members of our board of directors until the later of the end of the term of the Collaboration Agreement and November 23, 2018.

Stock-based Awards

Stock-based Awards	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	7. Stock-Based Awards Equity Plans In July 2015, we adopted the 2015 Stock Plan, or the 2015 Plan. Under the 2015 Plan, 4,681,544 shares of our common stock were initially reserved for the issuance of stock options and restricted stock to employees, directors, and consultants under terms and provisions established by the Board of Directors, or the Board, and approved by our stockholders. As of December 31, 2017 and December 31, 2016 there were 4,313,423 and 4,344,487 and shares available for future grant, respectively. Under the terms of the 2015 Plan, options may be granted at an exercise price not less than fair market value. For employees holding more than 10% of the voting rights of all classes of stock, the exercise prices for incentive stock options may not be less than 110% of fair market value, as determined by the Board. The terms of options granted under the 2015 Plan may not exceed ten years. All options issued to date have had a ten-year life. To date, options granted generally vest in three ways: 1) over four years at a rate of 25% upon the first anniversary of the issuance date and 1/48 th th th In August 2015, we adopted the 2015 Employee Stock Purchase Plan (the “2015 ESPP”), which commenced on January 1, 2018. Under the 2015 ESPP our employees may purchase common stock through payroll deductions at a price equal to 85% of the lower of the fair market value of the stock at the beginning of the offering period or at the end of each applicable purchase period. The 2015 ESPP generally provides for offering periods of six months in duration with purchase periods ending on either May 15 or November 15. Contributions under the 2015 ESPP are limited to a maximum of 15% of an employee’s eligible compensation. ESPP purchases are settled with common stock from the ESPP’s previously authorized and available pool of shares. Our 2013 Stock Plan, or the 2013 Plan, which was originally adopted during January 2013, was terminated upon consummation of our IPO in August 2015. As a terminated plan, no further options can be granted from the 2013 Plan, and no further shares are reserved for issuance under the 2013 Plan. Prior to its termination, the 2013 Plan allowed employees to exercise a stock option in exchange for cash before the requisite service is provided (e.g., before the award is vested under its original terms); however, such arrangements permit us to subsequently repurchase such shares at the exercise price if the vesting conditions are not satisfied. Such an exercise is not substantive for accounting purposes. Therefore, the payment received by us for the exercise price is recognized as an early exercise liability on the consolidated balance sheets and will be transferred to common stock and additional paid-in capital as such shares vest. As of December 31, 2017 and December 31, 2016, 46,973 and 199,538 unvested shares were legally issued and outstanding, respectively. In connection with these unvested shares, we have recorded an early exercise liability as of December 31, 2017 and 2016 of $7,000 and $62,000, respectively, of which $7,000 and $55,000 is included in other current liabilities as of December 31, 2017 and 2016, respectively, with the remaining was included in other liabilities in the consolidated balance sheets. These shares are excluded from basic and diluted net loss per share until our repurchase right lapses and the shares are no longer subject to the repurchase feature. Activity under the 2015 Plan and 2013 Plan is set forth below: Options Outstanding Number Options and Unvested Shares Weighted- Average Exercise Price Weighted Average Remaining Contractual Life (In years) Aggregate Intrinsic Value (In thousands) Balance, December 31, 2016 5,628,907 $ 9.50 9.0 $ 61,617 Options granted 2,371,700 $ 20.99 Options exercised and shares vested (1,021,997 ) $ 6.38 Options cancelled (349,499 ) $ 8.44 Balance, December 31, 2017 6,629,111 $ 14.15 8.2 $ 156,900 Options vested and expected to vest as of December 31, 2017 6,373,599 $ 13.98 8.2 $ 151,949 Options exercisable as of December 31, 2017 3,241,314 $ 8.77 8.2 $ 94,168 The aggregate intrinsic values of options outstanding, exercisable, and vested and expected to vest were calculated as the difference between the exercise price of the options and the market price for shares of our common stock as of December 31, 2017. The 2013 Plan provided for early exercise, therefore, all of the outstanding stock options issued under that plan are exercisable. The total intrinsic value of options exercised during the year ended December 31, 2017 was $17.9 million. Stock Awards Granted Stock options granted during the years ended December 31, 2017, 2016, and 2015 had a per share weighted-average grant-date fair value of $13.70, $10.53 and $6.11, respectively. The fair value is being expensed over the vesting period of the options, which is either four years or two years on a straight-line basis as the services are being provided. No tax benefits were realized from options during the periods. We issued one grant totaling 213,354 options to a non-employee during the year ended December 31, 2015. The fair value of the non-employee options was measured using the Black-Scholes option-pricing model reflecting the same assumptions as applied to employee options, other than the expected life, which was assumed to be the remaining contractual life of the option. During 2016, we converted the non-employee to an employee, and converted the grant from a non-employee grant to an employee grant. The conversion of the grant was treated as a modification of the original grant; accordingly, for the year ended December 31, 2016, we recognized $0.1 million of modification expense. As of December 31, 2017 and 2016, total unrecognized stock-based compensation expense related to options was $43.2 million and $27.3 million, respectively, which is expected to be recognized over the weighted-average remaining vesting period of 2.4 years and 2.7 years, respectively. Restricted stock unit, or RSU, activity under the 2015 Plan is set forth below: Shares Weighted Grant Date Fair Value Unvested Balance, December 31, 2016 17,000 $ 14.01 Awarded 16,638 35.41 Released (17,000 ) 14.01 Forfeited — — Unvested Balance, December 31, 2017 16,638 $ 35.41 RSUs are measured based on the fair market value of the underlying stock on the date of grant and recognized as expense on a straight-line basis over the employee’s requisite service period (generally the vesting period). As of December 31, 2017 and 2016, total unrecognized stock-based compensation expense related to RSUs was $0.6 million and $0.1 million, respectively, which is expected to be recognized over the weighted-average remaining vesting period of 3.7 years and 0.2 years, respectively. Determining Fair Value of Stock Options In determining the fair value of the stock options used to calculate stock-based compensation expense, we use the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires judgment to determine. • Expected Term. The expected term of stock options represents the weighted average period the stock options are expected to be outstanding. We have opted to use the simplified method for estimating the expected term as provided by the Securities and Exchange Commission Staff Accounting Bulletin, SAB, 110 as our options grants are considered “plain vanilla”. The simplified method calculates the expected term as the average time- to-vesting and the contractual life of the options. We plan to continue to use the simplified method under SAB 110 until we have sufficient exercise history as a publicly traded company. • Expected Volatility. As we have limited trading history for our common stock, the expected stock price volatility assumption is determined based on the historical volatilities of a group of industry peers as well as the historical volatility of our own common stock since we began trading subsequent to our IPO in August 2015. Industry peers consist of several public companies in the biopharmaceutical industry with comparable characteristics including enterprise value, risk profiles and position within the industry. We intend to continue to consistently apply this process using the same or similar public companies until a sufficient amount of historical information regarding the volatility of our own common stock share price becomes available, or unless circumstances change such that the identified companies are no longer similar to us, in which case, more suitable companies whose share prices are publicly available would be utilized in the calculation. • Risk-Free Interest Rate. The risk-free interest rate is based on the Black-Scholes valuation model on the implied yield available on U.S. Treasury zero-coupon issues in effect at the time of grant for periods corresponding with the expected term of the option. • Expected Dividend Yield. We have never paid dividends on our common stock and have no plans to pay dividends on our common stock. Therefore, we used an expected dividend yield of zero. The weighted-average assumptions used to estimate the fair value of stock options using the Black-Scholes option valuation model and the resulting weighted average grant date fair value of stock options granted were as follows: Year Ended December 31, 2017 2016 2015 Expected volatility 73.1 % 74.5 % 74.1 % Risk-free interest rate 2.0 % 1.7 % 1.7 % Expected dividend yield — — — Expected term (in years) 6.0 6.0 6.0 Weighted average grant date fair value $ 13.70 $ 10.53 $ 6.11 Stock-based compensation expense, net of estimated forfeitures, is reflected in the consolidated statements of operations and comprehensive loss (in thousands) as summarized below: Year Ended December 31, 2017 2016 2015 Research and development $ 5,077 $ 4,838 $ 2,522 General and administrative 11,642 7,803 3,635 Total stock-based compensation expense $ 16,719 $ 12,641 $ 6,157 During the years ended December 31, 2017, 2016 and 2015, we recorded $0.4 million, $0.9 million and $1.4 million of stock compensation expense related to the acceleration of certain former executives’ stock options, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes The following table presents loss before provision for income taxes (in thousands): Year Ended December 31, 2017 2016 2015 Income/(loss) before income taxes Domestic $ (100,107 ) $ (66,210 ) $ (17,489 ) Foreign (31,162 ) (14,614 ) (18,327 ) Total loss before provision for income taxes $ (131,269 ) $ (80,824 ) $ (35,816 ) The federal, state and foreign income tax provisions for the years ended December 31, 2017, 2016 and 2015 are summarized as follows (in thousands): Year Ended December 31, 2017 2016 2015 Current Federal $ — $ — $ — State — — — Foreign 56 — — Total Current 56 — — Deferred Federal — — — State — — — Foreign — — — Total Deferred — — — Total provision for income taxes $ 56 $ — $ — On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “2017 Tax Act”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a federal corporate tax rate decrease from 34% to 21% for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the mandatory deemed repatriation of foreign earnings. The 2017 Tax Act had no impact on tax expense primarily due to us maintaining a full valuation allowance against our net deferred tax assets. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 ("SAB 118") to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed in reasonable detail to complete the accounting for certain income tax effects of the 2017 Tax Act. We did not identify items for which the income tax effects of the 2017 Tax Act have not been completed and could not be reasonably estimated as of December 31, 2017, and as such, our financial results reflect the income tax effects of the 2017 Tax Act for which the accounting under ASC Topic 740 is complete. Income tax expense for the years ended December 31, 2017, 2016 and 2015 differed from the amount expected by applying the statutory federal tax rate to the loss before taxes as summarized below (in thousands): Year Ended December 31, 2017 2016 2015 Federal tax benefit at statutory rate 34.00 % 34.00 % 34.00 % State tax benefit, net of federal benefit 0.54 % 0.39 % 3.02 % Stock compensation 1.72 % (1.75 )% (1.59 )% Change in valuation allowance (9.31 )% (27.45 )% (20.55 )% Research and development credits 1.70 % 2.53 % 2.52 % Foreign income taxed at different rates (8.11 )% (6.13 )% (17.40 )% Impact related to 2017 Tax Act (20.46 )% 0.00 % 0.00 % Other (0.12 )% (1.59 )% 0.00 % Income tax expense (0.04 )% 0.00 % 0.00 % The significant components of our deferred taxes are as follows (in thousands): Year Ended December 31, 2017 2016 Deferred tax assets (liabilities): Net operating loss carryforwards $ 38,626 $ 27,109 Start-up costs 740 1,282 Stock-based compensation 3,115 3,427 Tax credit carryforwards 6,353 3,585 Accruals 1,153 1,041 Other 35 22 Subtotal deferred tax assets 50,022 36,466 Less: valuation allowance (49,934 ) (36,466 ) Total deferred tax assets 88 — Basis differences in fixed assets (88 ) Net deferred income taxes $ — $ — We recognize deferred income taxes for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. We periodically evaluate the positive and negative evidence bearing upon realizability of our deferred tax assets. Based upon the weight of available evidence, which includes our historical operating performance, reported cumulative net losses since inception and difficulty in accurately forecasting our future results, we maintained a full valuation allowance on the net deferred tax assets as of December 31, 2017 and 2016. We remeasured our deferred tax assets and liabilities at the applicable tax rate of 21% in accordance with the 2017 Tax Act. The remeasurement resulted in a total decrease in the deferred tax assets of $26.9 million with an equal reduction to the valuation allowance recorded against our net deferred tax assets. As of December 31, 2017, we had net operating loss, or NOL, carryforwards for Federal, California and other state income tax purposes of $177.9 million, $12.0 million, and $11.5 million, respectively. As of December 31, 2016, we had NOL carryforwards for Federal, California and other state income tax purposes of $81.0 million, $12.0 million, and $2.4 million, respectively, which will begin to expire in 2031, 2031, and 2030, respectively, if not utilized. As of December 31, 2017, we had Federal and California research credit carryforwards of $6.7 million and $1.6 million, respectively. As of December 31, 2016, we had Federal and California research credit carryforward of approximately $3.9 million and $0.9 million, respectively. The Federal research credits will begin to expire in 2032, while the California research credits have no expiration date. Under Section 382 of the Internal Revenue Code of 1986, as amended, or the Code, if a corporation undergoes an “ownership change,” generally defined as a greater than 50 percentage point change (by value) in its equity ownership over a rolling three-year period, the corporation’s ability to use its pre-change net operating loss, or NOL, carryforwards to offset its post-change taxable income may be limited. Limitations may also apply to the utilization of other pre-change tax attributes as a result of an ownership change. Following the equity investment by Nestle Health Science in November 2016, we performed a Section 382 analysis and determined that we experienced multiple ownership changes under Section 382 of the Code prior to July 31, 2017. Utilization of the NOL and tax credit carryforwards are subject to a substantial annual limitation due to the ownership change limitations set forth in Internal Revenue Code Section 382 and similar state provisions. Such annual limitations could impact the utilization of NOL and tax credit carryforwards in the future. We experienced no significant permanent losses of tax attributes due to these ownership changes. In addition, we may experience more ownership changes under Section 382 of the Code as a result of future changes in our stock ownership, some of which may be outside our control. As a result, our ability to utilize NOL carryforwards or other tax attributes, such as research tax credits, in any taxable year may be further limited if we have experienced an ownership change. Tax benefits from uncertain tax positions are recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on technical merits. The amount recognized is measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon effective settlement. The following table summarizes the activity related to our unrecognized benefits (in thousands): Year Ended December 31, 2017 2016 Beginning balance - unrecognized tax benefit, gross $ 960 $ — Increases related to tax positions taken during a prior year — — Decreases related to a tax position taken during a prior year (2 ) — Increases related to tax positions taken during the current year 699 960 Decreases related to settlements with taxing authorities — — Decreases related to expiration of statute of limitations — — Ending balance - unrecognized tax benefits, gross $ 1,657 $ 960 At December 31, 2017, the unrecognized tax benefits for uncertain tax positions were offset against the deferred tax assets and would not affect the income tax rate if recognized due to our being in a valuation allowance position. Our policy is to include interest and penalties related to unrecognized tax benefits, if any, within the provision for taxes in the consolidated statements of operations. We did not accrue any interest or penalties for the years ended December 31, 2017 and 2016. We do not have any tax positions for which it is reasonably possible that the total amount of gross unrecognized tax benefits will significantly change within 12 months of December 31, 2017. We file federal, state and foreign income tax returns in jurisdictions with varying statutes of limitations. Due to our NOL carryforwards, our income tax returns remain subject to examination by federal and most state taxing authorities for all tax years.

Collaboration Agreement

Collaboration Agreement	12 Months Ended
	Dec. 31, 2017
Collaboration Agreement [Abstract]
Collaboration Agreement

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Defined Contribution Plan	9. Defined Contribution Plan We sponsor a 401(k) Plan, or the 401(k) Plan, which stipulates that eligible employees may contribute to the 401(k) Plan subject to certain limitations. We may match employee contributions in amounts to be determined at our sole discretion. To date, we have not made any matching contributions.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	10. Related Party Transactions In June 2017, Mark McDade, a member of our Board of Directors, joined the Board of Directors of MyHealthTeams, a private company that creates social networks for people living with chronic conditions by partnering with pharmaceutical and healthcare companies. We entered into an agreement with MyHealthTeams in 2015 under which they provide services to us. During the years ended December 31, 2017, 2016 and 2015, our payments to MyHealthTeams pursuant to such agreement were $0.2 million, $0.2 million and less than $0.1 million, respectively. At December 31, 2017 and 2016, there were no accrued liabilities due under the MyHealthTeams agreement.

Selected Quarterly Results of O

Selected Quarterly Results of Operations (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Results of Operations (Unaudited)	11. Selected Quarterly Results of Operations (Unaudited) The following table presents our unaudited quarterly financial data. Our quarterly results of operations for these periods are not necessarily indicative of our future results of operations. Quarter Ended March 31 June 30 September 30 December 31 2017 (In thousands, except per share data) Operating expenses: Research and development $ 17,417 $ 22,191 $ 21,063 $ 28,654 General and administrative 8,924 10,813 11,226 12,986 Total operating expenses 26,341 33,004 32,289 41,640 Loss from operations (26,341 ) (33,004 ) (32,289 ) (41,640 ) Interest income, net 471 507 497 530 Loss before provision for income taxes (25,870 ) (32,497 ) (31,792 ) (41,110 ) Provision for income taxes — — — 56 Net loss $ (25,870 ) $ (32,497 ) $ (31,792 ) $ (41,166 ) Net loss per common share, basic and diluted $ (0.52 ) $ (0.65 ) $ (0.63 ) $ (0.81 ) Quarter Ended March 31 June 30 September 30 December 31 2016 (In thousands, except per share data) Operating expenses: Research and development $ 9,976 $ 11,820 $ 15,888 $ 16,958 General and administrative 5,723 6,466 6,353 8,343 Total operating expenses 15,699 18,286 22,241 25,301 Loss from operations (15,699 ) (18,286 ) (22,241 ) (25,301 ) Interest income, net 176 147 155 225 Net loss $ (15,523 ) $ (18,139 ) $ (22,086 ) $ (25,076 ) Net loss per common share, basic and diluted $ (0.37 ) $ (0.43 ) $ (0.53 ) $ (0.55 )

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Preparation	Basis of Preparation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States, or U.S. GAAP, and include the accounts of our wholly-owned subsidiaries. All significant intercompany transactions have been eliminated. We operate in one reportable segment in the United States.
Foreign Currency Translation	Foreign Currency Translation Our functional currency and the functional currency of all of our subsidiaries is the United States dollar. Accordingly, monetary assets and liabilities in the non-functional currency of these subsidiaries are remeasured using exchange rates in effect at the end of the period. Costs in local currency are remeasured using average exchange rates for the period, except for costs related to those balance sheet items that are remeasured using historical exchange rates. The resulting remeasurement gains and losses are included in the consolidated statements of operations and comprehensive loss as incurred and have not been material for all periods presented.
Use of Estimates	Use of Estimates The preparation of the accompanying consolidated financial statements in accordance with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of costs and expenses during the reporting period. 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.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents, which are carried at estimated fair value, consist primarily of money market funds and certain available-for-sale investments with maturities of three months or less.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. We have one operating segment.
Concentration of Credit Risk	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, corporate securities, U.S. government securities and commercial paper. Bank deposits are primarily held by a single financial institution and these deposits may exceed insured limits. We are exposed to credit risk in the event of default by the financial institution 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.
Investments	Investments Our investments consist of available-for-sale securities. Investments with original maturities of greater than 90 days but less than one (1) year are classified as short-term on the consolidated balance sheets. Investments with original maturities greater than one (1) year are classified as long-term on the consolidated balance sheets. Our investments in available-for-sale securities are reported at estimated fair value. Available-for-sale securities consist primarily of agency securities, corporate securities, U.S. government securities and commercial paper. Unrealized gains and losses related to changes in the fair value of securities are recognized in accumulated other comprehensive loss, net of tax, on our consolidated balance sheets. Changes in the fair value of available-for-sale securities impact the consolidated statements of operations and comprehensive loss only when such securities are sold or an other-than-temporary impairment is recognized. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. We regularly review our investment portfolio to determine if any security is other-than-temporarily impaired, which would require us to record an impairment charge in the period any such determination is made. We consider factors such as the duration, severity and the reason for the decline in value, the financial condition of the issuer and any changes thereto, the potential recovery period and our intent to sell. For debt securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis, and (ii) the amortized cost basis cannot be recovered as a result of credit losses. Our assessment on whether a security is other-than-temporarily impaired could change in the future due to new developments or changes in assumptions related to any particular security.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets. Maintenance and repairs are charged to the consolidated statements of operations and comprehensive loss as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss, if any, is reflected in the consolidated statements of operations and comprehensive loss. The useful lives of property and equipment are as follows: Furniture and office equipment 4 years Computer equipment 3 years Buildings 25 years Fixtures 10 years Leasehold improvements Shorter of remaining lease terms or useful life
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We evaluate our long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows expected to result from the use of the asset and its eventual disposition. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired assets. We have not recorded impairment of any long-lived assets in the periods presented.
Leases	Leases Leases related to our corporate headquarters are classified as operating leases. Rent expense is recognized on a straight-line basis over the terms of the leases and, accordingly, we record the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Incentives granted under facilities leases are deferred and recognized as adjustments to rental expense on a straight-line basis over the term of the lease. In June 2015, we signed a lease for a manufacturing facility in Clearwater, Florida. We were considered the deemed owner for accounting purposes. See Note 5, “Commitments and Contingencies,” for further details.
Research and Development	Research and Development We expense research and development costs as incurred. We record accrued liabilities for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of pre-clinical studies and clinical trials and contract manufacturing activities. These costs are a significant component of our research and development expenses. We accrue for these costs based on factors such as estimates of the work completed and in accordance with agreements established with our third-party service providers under the service agreements. We make significant judgments and estimates in determining the accrued liabilities balance in each reporting period. As actual costs become known, we adjust our accrued liabilities. We have not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled and the rate of patient enrollments may vary from our estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to our accruals could materially affect our results of operations.
Stock-based Compensation	Stock-Based Compensation Stock-based awards issued to employees, including stock options, are measured at fair value on the grant date using the Black--Scholes option-pricing model for stock options and the market price of our ordinary shares on that date for restricted stock units (“RSUs”). The fair value stock-based awards is
Income Taxes	Income Taxes We use the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of reported assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. We must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to our lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. Tax benefits from uncertain tax positions are recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on technical merits. The amount recognized is measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon effective settlement.
Comprehensive Income or Loss	Comprehensive Income or Loss Comprehensive income or loss is defined as the change in equity during a period from transactions and other events, excluding changes resulting from investments from owners and distributions to owners. Other comprehensive loss includes net loss and unrealized gains and losses on available-for-sale investments.
Net Loss per Share	Net Loss per Share The following common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive: Year Ended December 31, 2017 2016 2015 Series A convertible preferred stock — — — Stock options 6,629,111 5,429,267 4,814,892 Restricted stock units 16,638 17,000 —
Offering Costs	Offering Costs Offering costs represent underwriting, legal, accounting and other direct costs related to our IPO. These costs were deferred until completion of the IPO, at which time they were reclassified to additional paid-in capital as a reduction of the proceeds.
Fair Value Measurements	Fair Value Measurements We define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Our valuation techniques are based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect our market assumptions. We classify these inputs into the following hierarchy: Level 1 —Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; 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 significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Financial instruments include cash equivalents, investments, accounts payable, and accrued liabilities. Our cash equivalents and investments are carried at estimated fair value and remeasured on a recurring basis. The carrying value of accounts payable and accrued liabilities approximate their estimated fair value due to the relatively short-term nature of these instruments. Our valuation techniques used to measure the fair value of money market funds were derived from quoted prices in active markets for identical assets. The valuation techniques used to measure the fair value of investments, all of which have counterparties with high credit ratings, were valued based on quoted market prices or model-driven valuations using significant inputs derived from or corroborated by observable market data. In accordance with fair value accounting requirements, companies may choose to measure eligible financial instruments and certain other items at fair value. We have not elected the fair value option for any eligible financial instruments.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In March 2016, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2016-09, Compensation—Stock Compensation (Topic 718) Improvements to Employee Share-Based Payment Accounting , which simplifies several aspects of accounting for share-based payment transactions including the income tax consequences, classification of awards as either equity or liabilities, classification on the statement of cash flows and accounting for forfeitures. Upon our adoption of the new standard for fiscal year 2017, all excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in the income statement. The tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. We recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. We applied the modified retrospective approach upon adoption, and prior periods have not been adjusted. As a result, we have established a net operating loss deferred tax asset of $1.2 million to account for prior period excess tax benefits through retained earnings; however, an offsetting valuation allowance of $1.2 million has also been established through retained earnings because it is not more likely than not that the deferred asset will be realized due to historical and expected future losses, such that there is no impact on our consolidated financial statements. Additionally, as allowed by the standard, we elected to continue to estimate potential forfeitures.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting In November 2016, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2016-18, Statement of Cash Flows – Restricted Cash (Topic 230) In October 2016, the FASB, issued ASU, 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers Other Than Inventory In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In February 2016, the FASB, issued ASU, No. 2016-02, Leases (Topic 842)

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of Useful Lives of Property and Equipment	The useful lives of property and equipment are as follows: Furniture and office equipment 4 years Computer equipment 3 years Buildings 25 years Fixtures 10 years Leasehold improvements Shorter of remaining lease terms or useful life
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share	The following common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive: Year Ended December 31, 2017 2016 2015 Series A convertible preferred stock — — — Stock options 6,629,111 5,429,267 4,814,892 Restricted stock units 16,638 17,000 —

Available-for-Sale Securities22

Available-for-Sale Securities and Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Summary of Financial Instruments Measured at Fair Value on a Recurring Basis	The following table sets forth our financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Cash and cash equivalents: Cash and money market funds $ 39,072 $ — $ — $ 39,072 Corporate securities — 999 — 999 Commercial paper — 33,416 — 33,416 Total cash and cash equivalents $ 39,072 $ 34,415 $ — $ 73,487 Investments: Agency securities — 12,718 — 12,718 Corporate securities — 28,345 — 28,345 Commercial paper — 21,432 — 21,432 US government securities — 46,448 — 46,448 Total investments $ — $ 108,943 $ — $ 108,943 December 31, 2016 Level 1 Level 2 Level 3 Total Cash and cash equivalents: Cash and money market funds $ 107,977 $ — $ — $ 107,977 Commercial paper — 16,033 — 16,033 Total cash and cash equivalents $ 107,977 $ 16,033 $ — $ 124,010 Investments: Agency securities $ — $ 45,571 $ — $ 45,571 Corporate securities — 22,031 — 22,031 Commercial paper — 8,669 — 8,669 US government securities — 82,252 — 82,252 Total investments $ — $ 158,523 $ — $ 158,523
Summary of Aggregate Market Value, Cost Basis and Gross Unrealized Gains and Losses of Available-for-Sale Investments by Security Type	The aggregate market value, cost basis, and gross unrealized gains and losses of available-for-sale investments by security type, classified in cash equivalents and investments, as of December 31, 2017 and December 31, 2016 are as are as follows (in thousands): December 31, 2017 Amortized Cost Gross unrealized gains Gross unrealized losses Total fair value Agency securities $ 12,729 $ — $ (11 ) $ 12,718 Corporate securities 29,369 1 (26 ) 29,344 Commercial paper 54,848 — — 54,848 US government securities 46,520 — (72 ) 46,448 Total available-for-sale investments $ 143,466 $ 1 $ (109 ) $ 143,358 December 31, 2016 Amortized Cost Gross unrealized gains Gross unrealized losses Total fair value Agency securities $ 45,591 $ 5 $ (25 ) $ 45,571 Corporate securities 22,050 2 (21 ) 22,031 Commercial paper 24,702 — — 24,702 US government securities 82,240 15 (3 ) 82,252 Total available-for-sale investments $ 174,583 $ 22 $ (49 ) $ 174,556

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Summary of Property And Equipment, Net	Property and equipment, net consists of the following (in thousands): Year Ended December 31, 2017 2016 Furniture and equipment $ 1,655 $ 776 Computer equipment 1,410 850 Manufacturing equipment 830 703 Leased equipment 100 — Leasehold improvements 2,685 — Buildings 688 — Construction in progress 11,490 8,749 Property and equipment, gross 18,858 11,078 Less: accumulated depreciation (1,653 ) (687 ) Property and equipment, net $ 17,205 $ 10,391
Summary of Accrued Liabilities	Accrued liabilities consist of the following (in thousands): Year Ended December 31, 2017 2016 Compensation and benefits $ 6,205 $ 3,195 Research and development 12,716 5,154 Professional and consulting 2,370 967 Other 187 605 Total accrued liabilities $ 21,478 $ 9,921

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Aggregate Minimum Lease Payments	Total future aggregate minimum lease payments under our operating leases, are as follows (in thousands): Year Ended December 31, 2018 $ 2,985 2019 2,557 2020 2,645 2021 2,724 2022 2,805 and thereafter 4,611 Total $ 18,327
Schedule of Future Minimum Lease Payments Due under Capital Lease Obligation	The following is a schedule of future minimum lease payments due under the capital lease obligation as of December 31, 2017 (in thousands): Year Ended December 31, 2018 $ 33 2019 33 2020 34 2021 35 2022 9 Total capital lease obligation 144 Less: amount representing interest (53 ) Present value of net minimum capital lease payments 91 Less: current portion (14 ) Total noncurrent capital lease obligation $ 77

Stock-based Awards (Tables)

Stock-based Awards (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity	Activity under the 2015 Plan and 2013 Plan is set forth below: Options Outstanding Number Options and Unvested Shares Weighted- Average Exercise Price Weighted Average Remaining Contractual Life (In years) Aggregate Intrinsic Value (In thousands) Balance, December 31, 2016 5,628,907 $ 9.50 9.0 $ 61,617 Options granted 2,371,700 $ 20.99 Options exercised and shares vested (1,021,997 ) $ 6.38 Options cancelled (349,499 ) $ 8.44 Balance, December 31, 2017 6,629,111 $ 14.15 8.2 $ 156,900 Options vested and expected to vest as of December 31, 2017 6,373,599 $ 13.98 8.2 $ 151,949 Options exercisable as of December 31, 2017 3,241,314 $ 8.77 8.2 $ 94,168
Restricted Stock Unit Activity	Restricted stock unit, or RSU, activity under the 2015 Plan is set forth below: Shares Weighted Grant Date Fair Value Unvested Balance, December 31, 2016 17,000 $ 14.01 Awarded 16,638 35.41 Released (17,000 ) 14.01 Forfeited — — Unvested Balance, December 31, 2017 16,638 $ 35.41
Schedule of Weighted Average Assumptions to Fair Value of Stock Options	The weighted-average assumptions used to estimate the fair value of stock options using the Black-Scholes option valuation model and the resulting weighted average grant date fair value of stock options granted were as follows: Year Ended December 31, 2017 2016 2015 Expected volatility 73.1 % 74.5 % 74.1 % Risk-free interest rate 2.0 % 1.7 % 1.7 % Expected dividend yield — — — Expected term (in years) 6.0 6.0 6.0 Weighted average grant date fair value $ 13.70 $ 10.53 $ 6.11
Summary of Stock-based Compensation Expense Net of Estimated Forfeitures	Stock-based compensation expense, net of estimated forfeitures, is reflected in the consolidated statements of operations and comprehensive loss (in thousands) as summarized below: Year Ended December 31, 2017 2016 2015 Research and development $ 5,077 $ 4,838 $ 2,522 General and administrative 11,642 7,803 3,635 Total stock-based compensation expense $ 16,719 $ 12,641 $ 6,157

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Loss Before Provision for Income Taxes	The following table presents loss before provision for income taxes (in thousands): Year Ended December 31, 2017 2016 2015 Income/(loss) before income taxes Domestic $ (100,107 ) $ (66,210 ) $ (17,489 ) Foreign (31,162 ) (14,614 ) (18,327 ) Total loss before provision for income taxes $ (131,269 ) $ (80,824 ) $ (35,816 )
Summary of Federal, State and Foreign Income Tax Provisions	The federal, state and foreign income tax provisions for the years ended December 31, 2017, 2016 and 2015 are summarized as follows (in thousands): Year Ended December 31, 2017 2016 2015 Current Federal $ — $ — $ — State — — — Foreign 56 — — Total Current 56 — — Deferred Federal — — — State — — — Foreign — — — Total Deferred — — — Total provision for income taxes $ 56 $ — $ —
Summary of Income Tax Expense Differed from Statutory Federal Tax Rate to the Loss Before Taxes	Income tax expense for the years ended December 31, 2017, 2016 and 2015 differed from the amount expected by applying the statutory federal tax rate to the loss before taxes as summarized below (in thousands): Year Ended December 31, 2017 2016 2015 Federal tax benefit at statutory rate 34.00 % 34.00 % 34.00 % State tax benefit, net of federal benefit 0.54 % 0.39 % 3.02 % Stock compensation 1.72 % (1.75 )% (1.59 )% Change in valuation allowance (9.31 )% (27.45 )% (20.55 )% Research and development credits 1.70 % 2.53 % 2.52 % Foreign income taxed at different rates (8.11 )% (6.13 )% (17.40 )% Impact related to 2017 Tax Act (20.46 )% 0.00 % 0.00 % Other (0.12 )% (1.59 )% 0.00 % Income tax expense (0.04 )% 0.00 % 0.00 %
Significant Components of the Company's Deferred Taxes	The significant components of our deferred taxes are as follows (in thousands): Year Ended December 31, 2017 2016 Deferred tax assets (liabilities): Net operating loss carryforwards $ 38,626 $ 27,109 Start-up costs 740 1,282 Stock-based compensation 3,115 3,427 Tax credit carryforwards 6,353 3,585 Accruals 1,153 1,041 Other 35 22 Subtotal deferred tax assets 50,022 36,466 Less: valuation allowance (49,934 ) (36,466 ) Total deferred tax assets 88 — Basis differences in fixed assets (88 ) Net deferred income taxes $ — $ —
Summary of Activity Related to Unrecognized Benefits	The following table summarizes the activity related to our unrecognized benefits (in thousands): Year Ended December 31, 2017 2016 Beginning balance - unrecognized tax benefit, gross $ 960 $ — Increases related to tax positions taken during a prior year — — Decreases related to a tax position taken during a prior year (2 ) — Increases related to tax positions taken during the current year 699 960 Decreases related to settlements with taxing authorities — — Decreases related to expiration of statute of limitations — — Ending balance - unrecognized tax benefits, gross $ 1,657 $ 960

Selected Quarterly Results of27

Selected Quarterly Results of Operations (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Unaudited Quarterly Financial Data	The following table presents our unaudited quarterly financial data. Our quarterly results of operations for these periods are not necessarily indicative of our future results of operations. Quarter Ended March 31 June 30 September 30 December 31 2017 (In thousands, except per share data) Operating expenses: Research and development $ 17,417 $ 22,191 $ 21,063 $ 28,654 General and administrative 8,924 10,813 11,226 12,986 Total operating expenses 26,341 33,004 32,289 41,640 Loss from operations (26,341 ) (33,004 ) (32,289 ) (41,640 ) Interest income, net 471 507 497 530 Loss before provision for income taxes (25,870 ) (32,497 ) (31,792 ) (41,110 ) Provision for income taxes — — — 56 Net loss $ (25,870 ) $ (32,497 ) $ (31,792 ) $ (41,166 ) Net loss per common share, basic and diluted $ (0.52 ) $ (0.65 ) $ (0.63 ) $ (0.81 ) Quarter Ended March 31 June 30 September 30 December 31 2016 (In thousands, except per share data) Operating expenses: Research and development $ 9,976 $ 11,820 $ 15,888 $ 16,958 General and administrative 5,723 6,466 6,353 8,343 Total operating expenses 15,699 18,286 22,241 25,301 Loss from operations (15,699 ) (18,286 ) (22,241 ) (25,301 ) Interest income, net 176 147 155 225 Net loss $ (15,523 ) $ (18,139 ) $ (22,086 ) $ (25,076 ) Net loss per common share, basic and diluted $ (0.37 ) $ (0.43 ) $ (0.53 ) $ (0.55 )

Formation and Business of the28

Formation and Business of the Company - Additional Information (Details) $ / shares in Units, $ in Thousands	Nov. 23, 2016USD ($)shares	Aug. 11, 2015USD ($)$ / sharesshares	Jul. 30, 2015shares	Dec. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)$ / sharesshares	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)
Organization And Description Of Business [Line Items]
Net loss | $				$ 41,166	$ 31,792	$ 32,497	$ 25,870	$ 25,076	$ 22,086	$ 18,139	$ 15,523	$ 131,325	$ 80,824	$ 35,816
Net cash used in operating activities | $												99,605	56,614	35,690
Accumulated deficit | $				265,482				$ 134,157				265,482	134,157
Cash, cash equivalents and investments | $				$ 182,400								182,400
Proceeds from issuance of common stock | $												$ 6,520	$ 145,000	$ 168,119
Proceeds from initial public offering, net of underwriting discount and commissions | $		$ 168,100
Common stock, shares outstanding				51,091,000				50,204,000				51,091,000	50,204,000
Description of stock split												On July 30, 2015, we effected a 1-for-1.317 stock split of our common stock and convertible preferred stock.
Stock split conversion ratio			0.7593
Common stock, shares authorized			55,051,264	290,000,000				290,000,000				290,000,000	290,000,000
Preferred stock, shares authorized			25,051,264	10,000,000				10,000,000				10,000,000	10,000,000
Common stock, par value | $ / shares				$ 0.0001				$ 0.0001				$ 0.0001	$ 0.0001
Preferred stock, par value | $ / shares				$ 0.0001				$ 0.0001				$ 0.0001	$ 0.0001
Private Placement | NHScUS
Organization And Description Of Business [Line Items]
Issuance of common stock upon securities purchase agreement	7,522,084
Proceeds from issuance of common stock | $	$ 145,000
IPO
Organization And Description Of Business [Line Items]
Common stock, shares issued		11,499,999
Common stock issued price per share | $ / shares		$ 16
Shares issued pursuant to exercise of underwriters' option		1,499,999
Outstanding shares of convertible preferred stock converted into common stock		25,051,257
Common stock, shares outstanding				51,090,813								51,090,813
Common stock, shares authorized		290,000,000
Preferred stock, shares authorized		10,000,000
Common stock, par value | $ / shares		$ 0.0001
Preferred stock, par value | $ / shares		$ 0.0001

Summary of Significant Accoun29

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017USD ($)Segmentshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares
Significant Accounting Policies [Line Items]
Number of reportable segments | Segment	1
Number of operating segments | Segment	1
Impairment of any long lived assets	$ 0	$ 0	$ 0
Stock options granted | shares	2,371,700	2,343,385	4,192,485
Deferred Tax Asset | Retained Earnings | ASU 2016-09
Significant Accounting Policies [Line Items]
Cumulative effect adjustment to retained earnings	$ 1,200,000
Offsetting Valuation Allowance | Retained Earnings | ASU 2016-09
Significant Accounting Policies [Line Items]
Cumulative effect adjustment to retained earnings	$ 1,200,000
Minimum
Significant Accounting Policies [Line Items]
Tax benefit recognized upon effective settlement percentage	50.00%
Restricted Stock Units
Significant Accounting Policies [Line Items]
Restricted stock units awarded | shares	16,638	17,000	0

Summary of Significant Accoun30

Summary of Significant Accounting Policies - Schedule of Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Furniture And Office Equipment
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	4 years
Computer Equipment
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	3 years
Buildings
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	25 years
Fixtures
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	10 years
Leasehold improvements
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	Shorter of remaining lease terms or useful life

Summary of Significant Accoun31

Summary of Significant Accounting Policies -Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	6,629,111	5,429,267	4,814,892
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	16,638	17,000

Available-for-Sale Securities32

Available-for-Sale Securities and Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - Fair Value Measurements Recurring - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Cash and cash equivalents
Total cash and cash equivalents	$ 73,487	$ 124,010
Investments:
Total investments	108,943	158,523
Commercial Paper
Cash and cash equivalents
Total cash and cash equivalents	33,416	16,033
Investments:
Total investments	21,432	8,669
US Government Securities
Investments:
Total investments	46,448	82,252
Corporate Debt Securities
Cash and cash equivalents
Total cash and cash equivalents	999
Investments:
Total investments	28,345	22,031
Agency Securities
Investments:
Total investments	12,718	45,571
Cash and money market funds
Cash and cash equivalents
Total cash and cash equivalents	39,072	107,977
Level 1
Cash and cash equivalents
Total cash and cash equivalents	39,072	107,977
Level 1 | Cash and money market funds
Cash and cash equivalents
Total cash and cash equivalents	39,072	107,977
Level 2
Cash and cash equivalents
Total cash and cash equivalents	34,415	16,033
Investments:
Total investments	108,943	158,523
Level 2 | Commercial Paper
Cash and cash equivalents
Total cash and cash equivalents	33,416	16,033
Investments:
Total investments	21,432	8,669
Level 2 | US Government Securities
Investments:
Total investments	46,448	82,252
Level 2 | Corporate Debt Securities
Cash and cash equivalents
Total cash and cash equivalents	999
Investments:
Total investments	28,345	22,031
Level 2 | Agency Securities
Investments:
Total investments	$ 12,718	$ 45,571

Available-for-Sale Securities33

Available-for-Sale Securities and Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair value assets transfers between level 1 to level 2	$ 0	$ 0
Fair value assets transfers between level 2 to level 1	$ 0	0
Available-for-sale securities, maturities period	1 year
Other than temporary impairment losses	$ 0	$ 0	$ 0
Marketable securities unrealized losses position maximum period	12 months

Available-for-Sale Securities34

Available-for-Sale Securities and Fair Value Measurements - Summary of Aggregate Market Value, Cost Basis, and Gross Unrealized Gains and Losses of Available for Sale Investments by Security Type (Details) - Available-for-sale Securities - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	$ 143,466	$ 174,583
Grossunrealizedgains	1	22
Grossunrealized losses	(109)	(49)
Total Available-for-Sale Investments	143,358	174,556
Commercial Paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	54,848	24,702
Total Available-for-Sale Investments	54,848	24,702
US Government Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	46,520	82,240
Grossunrealizedgains		15
Grossunrealized losses	(72)	(3)
Total Available-for-Sale Investments	46,448	82,252
Corporate Debt Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	29,369	22,050
Grossunrealizedgains	1	2
Grossunrealized losses	(26)	(21)
Total Available-for-Sale Investments	29,344	22,031
Agency Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	12,729	45,591
Grossunrealizedgains		5
Grossunrealized losses	(11)	(25)
Total Available-for-Sale Investments	$ 12,718	$ 45,571

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 18,858	$ 11,078
Less: accumulated depreciation	(1,653)	(687)
Property and equipment, net	17,205	10,391
Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,655	776
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,410	850
Manufacturing equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	830	703
Leased equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	100
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,685
Buildings
Property Plant And Equipment [Line Items]
Property and equipment, gross	688
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 11,490	$ 8,749

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance Sheet Related Disclosures [Abstract]
Depreciation Expense	$ 966	$ 534	$ 115

Balance Sheet Components - Su37

Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities Current [Abstract]
Compensation and benefits	$ 6,205	$ 3,195
Research and development	12,716	5,154
Professional and consulting	2,370	967
Other	187	605
Total accrued liabilities	$ 21,478	$ 9,921

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended	12 Months Ended
	Jun. 30, 2015ft²	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Jun. 30, 2017ft²	Aug. 31, 2015ft²	Mar. 31, 2015USD ($)ft²
Commitments And Contingencies [Line Items]
Expected additional operating lease space possession date		Jan. 1, 2018
Lease, termination date		Jun. 30, 2024
Security deposit							$ 0
Term of capital lease agreement		5 years
Long-term purchase commitment, restated agreement effective period after first delivery		10 years
Long-term purchase commitment, shares issued, vesting period		3 years 6 months
Peanut Flour | Archer Daniels Midland Company
Commitments And Contingencies [Line Items]
Long-term purchase commitment amount		$ 8,300,000
Long-term purchase commitment period		10 years
Long-term purchase commitment, optional extension period		5 years
Long-term purchase commitment, shares issued | shares		300,000
Maximum
Commitments And Contingencies [Line Items]
Term of lease		12 months
Facility Leases
Commitments And Contingencies [Line Items]
Rent expense under operating leases		$ 2,400,000	$ 1,700,000	$ 600,000
Facility Leases | Corporate Headquarters
Commitments And Contingencies [Line Items]
Leased area | ft²					14,841	26,355	11,665
Facility Leases | Manufacturing Facility
Commitments And Contingencies [Line Items]
Leased area | ft²	20,000
Term of lease	120 months
Design costs related to building		13,300,000
Building shell construction cost capitalized		700,000
Construction in progress for costs incurred by the lessor		$ 10,400,000

Commitments and Contingencies39

Commitments and Contingencies - Future Aggregate Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,018	$ 2,985
2,019	2,557
2,020	2,645
2,021	2,724
2,022	2,805
and thereafter	4,611
Total	$ 18,327

Commitments and Contingencies40

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Due under Capital Lease Obligation (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,018	$ 33
2,019	33
2,020	34
2,021	35
2,022	9
Total capital lease obligation	144
Less: amount representing interest	(53)
Present value of net minimum capital lease payments	91
Less: current portion	(14)
Total noncurrent capital lease obligation	$ 77

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	Nov. 23, 2016	Jan. 31, 2015	Feb. 28, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 11, 2015	Jul. 30, 2015
Stockholders Equity [Line Items]
Preferred stock, shares issued				0	0
Preferred stock, par value				$ 0.0001	$ 0.0001
Preferred stock, shares authorized				10,000,000	10,000,000			25,051,264
Preferred stock, shares outstanding				0	0
Common stock, par value				$ 0.0001	$ 0.0001
Proceeds from issuance of common stock				$ 6,520,000	$ 145,000,000	$ 168,119,000
NHScUS | Purchase Agreement
Stockholders Equity [Line Items]
Issuance of common stock upon securities purchase agreement	7,522,084
Common stock, par value	$ 0.0001
Proceeds from issuance of common stock	$ 145,000,000
Initial Public Offering
Stockholders Equity [Line Items]
Preferred stock, par value							$ 0.0001
Outstanding shares of convertible preferred stock converted into common stock							25,051,257
Preferred stock, shares authorized							10,000,000
Common stock, par value							$ 0.0001
Series A Convertible Preferred Stock
Stockholders Equity [Line Items]
Stock repurchased from investors		2,260,706
Preferred stock, redemption price per share		$ 5.69
Repurchase of convertible preferred stock		$ 12,900,000				$ 12,874,000
Series B Convertible Preferred Stock
Stockholders Equity [Line Items]
Preferred stock, shares issued			14,047,996
Preferred stock, par value			$ 0.0001
Share price (per share)			$ 5.69			$ 5.69
Gross cash proceeds from preferred stock			$ 80,000,000
Offering costs for issuance and sale of convertible preferred stock						$ 221,000
Convertible Preferred Stock
Stockholders Equity [Line Items]
Preferred stock, shares issued				0	0
Preferred stock, shares authorized				10,000,000	10,000,000
Preferred stock, shares outstanding				0	0

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Details)	1 Months Ended		12 Months Ended
	Aug. 31, 2015	Jul. 31, 2015shares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)Grant$ / sharesshares	Jan. 31, 2013shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period			3 years 6 months
Unvested shares outstanding			6,629,111	5,628,907
Intrinsic Value of option exercised | $			$ 17,900,000
Stock option granted, per share weighted average grant-date fair value | $ / shares			$ 13.70	$ 10.53	$ 6.11
Number of shares available for grant			2,371,700	2,343,385	4,192,485
Expected dividend yield			0.00%
Former Executive
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Accelerated stock compensation expense | $			$ 400,000	$ 900,000	$ 1,400,000
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option granted, per share weighted average grant-date fair value | $ / shares			$ 13.70	$ 10.53	$ 6.11
Tax benefit realized from option | $			$ 0
Stock option grant modification expense | $				$ 100,000
Unrecognized employee stock-based compensation | $			$ 43,200,000	$ 27,300,000
Expected recognized over weighted-average remaining vesting period			2 years 4 months 24 days	2 years 8 months 12 days
Stock Options | Non-Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant					213,354
Number of grants issued | Grant					1
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized employee stock-based compensation | $			$ 600,000	$ 100,000
Expected recognized over weighted-average remaining vesting period			3 years 8 months 12 days	2 months 12 days
Maximum | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period			4 years
Minimum | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period			2 years
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares reserved for issuance		4,681,544
Number of shares available for future grant			4,313,423	4,344,487
Minimum percentage of voting rights of all classes of stock		10.00%
Percentage of statutory stock options		110.00%
Options expiration period		10 years
2015 Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options expiration period		10 years
2015 Plan | First Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period		4 years
Option vesting rights, percentage		25.00%
2015 Plan | Thereafter
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage		2.08%
2015 Plan | Over Two Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period		2 years
Option vesting rights, percentage		4.17%
2015 Plan | Over Four Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period		4 years
Option vesting rights, percentage		2.08%
2015 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of statutory stock options	85.00%
Description of ESPP			Under the 2015 ESPP our employees may purchase common stock through payroll deductions at a price equal to 85% of the lower of the fair market value of the stock at the beginning of the offering period or at the end of each applicable purchase period. The 2015 ESPP generally provides for offering periods of six months in duration with purchase periods ending on either May 15 or November 15. Contributions under the 2015 ESPP are limited to a maximum of 15% of an employee’s eligible compensation.
Percentage of maximum contributions employee's eligible compensation	15.00%
ESPP offering period	6 months
Description of offering period closing dates			The 2015 ESPP generally provides for offering periods of six months in duration with purchase periods ending on either May 15 or November 15.
2013 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares reserved for issuance			0			0
Number of shares available for future grant			0
Unvested shares issued			46,973	199,538
Unvested shares outstanding			46,973	199,538
Exercise liability | $			$ 7,000	$ 62,000
Exercise liability current | $			$ 7,000	$ 55,000

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Options and Unvested Shares
Number of Options and Unvested Shares, Beginning Balance	5,628,907
Number of Options and Unvested Shares, Options granted	2,371,700	2,343,385	4,192,485
Number of Options and Unvested Shares, Options exercised and shares vested	(1,021,997)
Number of Options and Unvested Shares, Options cancelled	(349,499)
Number of Options and Unvested Shares, Ending Balance	6,629,111	5,628,907
Number of Options and Unvested Shares, Options vested and expected to vest as of December 31, 2017	6,373,599
Number of Options and Unvested Shares, Options exercisable as of December 31, 2017	3,241,314
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Beginning Balance	$ 9.50
Weighted-Average Exercise Price, Options granted	20.99
Weighted-Average Exercise Price, Options exercised and shares vested	6.38
Weighted-Average Exercise Price, Options cancelled	8.44
Weighted-Average Exercise Price, Ending Balance	14.15	$ 9.50
Weighted-Average Exercise Price, Options vested and expected to vest as of December 31, 2017	13.98
Weighted-Average Exercise Price, Options exercisable as of December 31, 2017	$ 8.77
Weighted Average Remaining Contractual Life (In years)
Weighted Average Remaining Contractual Life (In years), Balance	8 years 2 months 12 days	9 years
Weighted Average Remaining Contractual Life, Options vested and expected to vest as of December 31, 2017	8 years 2 months 12 days
Weighted Average Remaining Contractual Life, Options exercisable as of December 31, 2017	8 years 2 months 12 days
Aggregate Intrinsic Value, Balance	$ 156,900	$ 61,617
Aggregate Intrinsic Value, Options vested and expected to vest as of December 31, 2017	151,949
Aggregate Intrinsic Value, Options exercisable as of December 31, 2017	$ 94,168

Stock-Based Awards - Restricted

Stock-Based Awards - Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Awarded	16,638	17,000	0
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested Shares, Beginning Balance	17,000
Shares, Awarded	16,638
Shares, Released	(17,000)
Unvested Shares, Ending Balance	16,638	17,000
Unvested Weighted Average Grant Date Fair Value, Beginning Balance	$ 14.01
Weighted Average Grant Date Fair Value, Awarded	35.41
Weighted Average Grant Date Fair Value, Released	14.01
Weighted Average Grant Date Fair Value, Ending Balance	$ 35.41	$ 14.01

Stock-Based Awards - Schedule o

Stock-Based Awards - Schedule of Weighted Average Assumptions to Fair Value of Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Expected volatility	73.10%	74.50%	74.10%
Risk-free interest rate	2.00%	1.70%	1.70%
Expected dividend yield	0.00%
Expected term (in years)	6 years	6 years	6 years
Weighted average grant date fair value	$ 13.70	$ 10.53	$ 6.11

Stock-Based Awards - Summary 46

Stock-Based Awards - Summary of Stock-based Compensation Expense Net of Estimated Forfeitures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 16,719	$ 12,641	$ 6,157
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	5,077	4,838	2,522
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 11,642	$ 7,803	$ 3,635

Income Taxes - Schedule of Loss

Income Taxes - Schedule of Loss Before Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income/(loss) before income taxes
Domestic					$ (100,107)	$ (66,210)	$ (17,489)
Foreign					(31,162)	(14,614)	(18,327)
Loss before provision for income taxes	$ (41,110)	$ (31,792)	$ (32,497)	$ (25,870)	$ (131,269)	$ (80,824)	$ (35,816)

Income Taxes - Summary of Feder

Income Taxes - Summary of Federal, State and Foreign Income Tax Provisions (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017
Current
Foreign		$ 56
Total Current		56
Deferred
Total provision for income taxes	$ 56	$ 56

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Federal corporate tax rate		34.00%	34.00%	34.00%
Decrease in deferred tax assets due to change in tax act		$ 26,900,000
Net change in valuation allowance		13,500,000	$ 22,100,000
Interest and penalties related to unrecognized tax benefits		0	0
Federal
Operating Loss Carryforwards [Line Items]
Operating loss, Net		$ 177,900,000	81,000,000
Net operating loss carryforward expiration year		2,031
Research credit carryforwards		$ 6,700,000	3,900,000
Research credit carryforward expiration year		2,032
Other State
Operating Loss Carryforwards [Line Items]
Operating loss, Net		$ 11,500,000	2,400,000
Net operating loss carryforward expiration year		2,030
California
Operating Loss Carryforwards [Line Items]
Operating loss, Net		$ 12,000,000	12,000,000
Net operating loss carryforward expiration year		2,031
Research credit carryforwards		$ 1,600,000	$ 900,000
Scenario, Forecast
Operating Loss Carryforwards [Line Items]
Federal corporate tax rate	21.00%

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Tax Expense Differed from Statutory Federal Tax Rate to the Loss Before Taxes (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal tax benefit at statutory rate	34.00%	34.00%	34.00%
State tax benefit, net of federal benefit	0.54%	0.39%	3.02%
Stock compensation	1.72%	(1.75%)	(1.59%)
Change in valuation allowance	(9.31%)	(27.45%)	(20.55%)
Research and development credits	1.70%	2.53%	2.52%
Foreign income taxed at different rates	(8.11%)	(6.13%)	(17.40%)
Impact related to 2017 Tax Act	(20.46%)	0.00%	0.00%
Other	(0.12%)	(1.59%)	0.00%
Income tax expense	(0.04%)	0.00%	0.00%

Income Taxes - Significant Comp

Income Taxes - Significant Components of the Company's Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets (liabilities):
Net operating loss carryforwards	$ 38,626	$ 27,109
Start-up costs	740	1,282
Stock-based compensation	3,115	3,427
Tax credit carryforwards	6,353	3,585
Accruals	1,153	1,041
Other	35	22
Subtotal deferred tax assets	50,022	36,466
Less: valuation allowance	(49,934)	$ (36,466)
Total deferred tax assets	88
Basis differences in fixed assets	$ (88)

Income Taxes - Summary of Activ

Income Taxes - Summary of Activity Related to Unrecognized Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Beginning balance - unrecognized tax benefit, gross	$ 960
Decreases related to a tax position taken during a prior year	(2)
Increases related to tax positions taken during the current year	699	$ 960
Ending balance - unrecognized tax benefits, gross	$ 1,657	$ 960

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - MyHealth Teams - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Payments to service agreement	$ 200,000	$ 200,000
Accrued liabilities due	$ 0	$ 0
Maximum
Related Party Transaction [Line Items]
Payments to service agreement			$ 100,000

Selected Quarterly Results of54

Selected Quarterly Results of Operations (Unaudited) - Schedule of Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses
Research and development	$ 28,654	$ 21,063	$ 22,191	$ 17,417	$ 16,958	$ 15,888	$ 11,820	$ 9,976	$ 89,325	$ 54,642	$ 19,816
General and administrative	12,986	11,226	10,813	8,924	8,343	6,353	6,466	5,723	43,949	26,885	16,181
Total operating expenses	41,640	32,289	33,004	26,341	25,301	22,241	18,286	15,699	133,274	81,527	35,997
Loss from operations	(41,640)	(32,289)	(33,004)	(26,341)	(25,301)	(22,241)	(18,286)	(15,699)	(133,274)	(81,527)	(35,997)
Interest income, net	530	497	507	471	225	155	147	176	2,005	703	181
Loss before provision for income taxes	(41,110)	(31,792)	(32,497)	(25,870)					(131,269)	(80,824)	(35,816)
Provision for income taxes	56								56
Net loss	$ (41,166)	$ (31,792)	$ (32,497)	$ (25,870)	$ (25,076)	$ (22,086)	$ (18,139)	$ (15,523)	$ (131,325)	$ (80,824)	$ (35,816)
Net loss per common share, basic and diluted	$ (0.81)	$ (0.63)	$ (0.65)	$ (0.52)	$ (0.55)	$ (0.53)	$ (0.43)	$ (0.37)	$ (2.61)	$ (1.89)	$ (1.88)