Alpine Immune Sciences (ALPN) 10-K 18 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Mar. 06, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	Alpine Immune Sciences, Inc.
Trading Symbol	ALPN
Entity Central Index Key	0001626199
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		18,561,029
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 33.8

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 10,711	$ 8,000
Short-term investments	41,592	73,240
Prepaid expenses and other current assets	1,242	1,308
Total current assets	53,545	82,548
Restricted cash	132	132
Property and equipment, net	1,196	1,089
Intangible assets	0	1,453
Total assets	54,873	85,222
Current liabilities:
Accounts payable	1,716	193
Accrued liabilities	4,277	382
Deferred revenue	0	277
Deferred rent, current portion	86	48
Current portion of long-term debt	2,048	995
Total current liabilities	8,127	1,895
Deferred rent, long-term portion	0	66
Deferred tax liability	0	305
Long-term debt	2,155	4,039
Total liabilities	10,282	6,305
Commitments and contingencies
Convertible preferred stock, $0.001 par value per share; 10,000,000 shares authorized at December 31, 2018 and 2017; zero shares issued and outstanding at December 31, 2018 and 2017	0	0
Stockholders’ equity:
Common stock, $0.001 par value per share; 200,000,000 shares authorized at December 31, 2018 and 2017; 13,904,672 shares issued and 13,854,205 shares outstanding at December 31, 2018; 13,881,645 shares issued and 13,831,178 shares outstanding at December 31, 2017	14	14
Treasury stock, at cost; 50,467 shares at December 31, 2018 and 2017	0	0
Additional paid-in capital	90,664	88,346
Accumulated other comprehensive loss	(13)	(59)
Accumulated deficit	(46,074)	(9,384)
Total stockholders’ equity	44,591	78,917
Total liabilities, convertible preferred stock, and stockholders’ equity	$ 54,873	$ 85,222

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Convertible preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Convertible preferred stock, shares issued (in shares)	0	0
Convertible preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	13,904,672	13,881,645
Common stock, shares outstanding (in shares)	13,854,205	13,831,178
Treasury stock, shares (in shares)	50,467	50,467

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Collaboration revenue	$ 705	$ 1,731	$ 2,950
Operating expenses:
Research and development	28,970	10,626	2,989
General and administrative	8,362	6,079	1,149
Loss on sale of intangible asset	1,203	0	0
Total operating expenses	38,535	16,705	4,138
Loss from operations	(37,830)	(14,974)	(1,188)
Other income (expense):
Bargain purchase gain	0	6,601	0
Interest expense	(319)	(152)	0
Interest and other income	1,296	542	22
Loss before taxes	(36,853)	(7,983)	(1,166)
Income tax benefit (expense)	366	200	(66)
Basic and diluted net loss attributable to common stockholders	(36,487)	(7,783)	(1,232)
Comprehensive income (loss):
Unrealized gain (loss) on investments	46	(59)	0
Comprehensive loss	$ (36,441)	$ (7,842)	$ (1,232)
Weighted-average shares used to compute basic and diluted net loss per share attributable to common stockholders (in shares)	13,849,470	6,481,665	564,816
Basic and diluted net loss per share attributable to common stockholders (in dollars per share)	$ (2.63)	$ (1.20)	$ (2.18)

Consolidated Statement of Conve

Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Treasury	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Convertible Preferred Stock
Balance, convertible preferred stock, shares (in shares) at Dec. 31, 2015							1,212,436
Balance, convertible preferred stock at Dec. 31, 2015							$ 610
Balance, shares issued (in shares) at Dec. 31, 2015		496,900	0
Balance at Dec. 31, 2015	$ (352)	$ 0	$ 0	$ 17	$ 0	$ (369)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of convertible preferred stock (in shares)							3,099,334
Issuance of convertible preferred stock	0						$ 10,925
Exercise of stock options (in shares)		111,801
Exercise of stock options	50			50
Stock-based compensation	77			77
Unrealized loss on investments	0
Net loss	(1,232)					(1,232)
Balance, convertible preferred stock, shares (in shares) at Dec. 31, 2016							4,311,770
Balance, convertible preferred stock at Dec. 31, 2016							$ 11,535
Balance, shares issued (in shares) at Dec. 31, 2016		608,701	0
Balance at Dec. 31, 2016	(1,457)	$ 0	$ 0	144	0	(1,601)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of convertible preferred stock (in shares)							4,989,663
Issuance of convertible preferred stock	0						$ 37,666
Conversion of convertible preferred stock to common stock (in shares)							(9,301,433)
Conversion of convertible preferred stock to common stock							$ (49,201)
Conversion of convertible preferred stock to common stock (in shares)		9,301,433
Conversion of convertible preferred stock to common stock	49,201	$ 1		49,200
Common stock acquired in business combination (in shares)		3,914,058
Common stock acquired in business combination	38,103			38,103
Adjustment of par value from $0.0001 per share to $0.001 per share	0	$ 13		(13)
Conversion of warrant liability to equity	52			52
Exercise of stock options and common stock warrants (in shares)		57,453
Exercise of stock options and common stock warrants	22			22
Repurchase of common stock (in shares)		50,467	50,467
Repurchase of common stock	0
Stock-based compensation	838			838
Unrealized loss on investments	(59)				(59)
Net loss	$ (7,783)					(7,783)
Balance, convertible preferred stock, shares (in shares) at Dec. 31, 2017	0						0
Balance, convertible preferred stock at Dec. 31, 2017	$ 0						$ 0
Balance, shares issued (in shares) at Dec. 31, 2017		13,831,178	50,467
Balance at Dec. 31, 2017	78,917	$ 14	$ 0	88,346	(59)	(9,384)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		23,027
Exercise of stock options	9			9
Stock-based compensation	2,309			2,309
Unrealized loss on investments	46				46
Net loss	$ (36,487)					(36,487)
Balance, convertible preferred stock, shares (in shares) at Dec. 31, 2018	0						0
Balance, convertible preferred stock at Dec. 31, 2018	$ 0						$ 0
Balance, shares issued (in shares) at Dec. 31, 2018		13,854,205	50,467
Balance at Dec. 31, 2018	$ 44,591	$ 14	$ 0	$ 90,664	$ (13)	$ (46,074)

Consolidated Statement of Con_2

Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.0001

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (36,487)	$ (7,783)	$ (1,232)
Adjustments to reconcile net loss to net cash used in operating activities:
Loss on sale of intangible asset	1,203	0	0
Bargain purchase gain	0	(6,601)	0
Depreciation expense	388	241	69
Amortization of premium/discount on investments	(669)	0	0
Non-cash interest expense	169	87	0
Deferred income tax	(305)	(204)	0
Stock-based compensation and warrant expense	2,309	838	77
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	66	(1,193)	(26)
Accounts payable	1,523	66	80
Deferred revenue	(480)	(1,731)	(2,950)
Accrued liabilities	3,895	(259)	39
Deferred rent and other	(28)	(33)	146
Net cash used in operating activities	(28,416)	(16,572)	(3,797)
Investing activities
Purchases of property and equipment	(495)	(586)	(782)
Proceeds from sale of intangible asset	250	0	0
Purchase of short-term investments	(72,863)	(88,307)	0
Maturities of short-term investments	105,226	0	0
Proceeds from the sale of short-term investments	0	27,960	0
Cash and cash equivalents acquired in connection with merger	0	31,130	0
Net cash provided by (used in) investing activities	32,118	(29,803)	(782)
Financing activities
Proceeds from sale of preferred stock	0	37,666	10,925
Proceeds from borrowings	0	5,000	0
Repayment of debt	(1,000)	0	0
Proceeds from exercise of stock options and common stock warrants	9	22	50
Net cash (used in) provided by financing activities	(991)	42,688	10,975
Net increase (decrease) in cash and cash equivalents and restricted cash	2,711	(3,687)	6,396
Cash and cash equivalents and restricted cash, beginning of period	8,132	11,819	5,423
Cash and cash equivalents and restricted cash, end of period	10,843	8,132	11,819
Supplemental Information
Convertible preferred stock exchanged for common stock	0	49,201	0
Discount in connection with issuance of debt	0	428	0
Cash paid for income taxes	0	76	0
Cash paid for interest	149	53	0
Reclass of preferred stock warrant liability to equity	$ 0	$ 52	$ 0

Description of Business

Description of Business	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business Alpine Immune Sciences, Inc. (the “Company”, “Alpine”, “we”, “us”, or “our”), together with its consolidated subsidiaries, is focused on discovering and developing innovative, protein-based immunotherapies targeting the immune synapse to treat cancer, autoimmune/inflammatory disorders, and other diseases. Our proprietary scientific platform uses a process known as directed evolution, or an iterative scientific engineering process purposefully conducted to “evolve” a protein to create multi-targeted therapeutics potentially capable of modulating the human immune system. In our pre-clinical animal studies, our platform has proven capable of identifying novel molecules, including single domains capable of modulating multiple targets. We were incorporated under the laws of the State of Delaware and are headquartered in Seattle, Washington. Reverse Merger and Subscription Agreement On April 18, 2017, we entered into a merger agreement with Nivalis Therapeutics, Inc. (“Nivalis”), a public biotechnology company, and one of its wholly-owned subsidiaries pursuant to which, the subsidiary merged with and into Alpine, with Alpine continuing as a wholly owned subsidiary of Nivalis and the surviving corporation of the merger (the “Merger Agreement”). Nivalis Therapeutics, Inc. was incorporated in Delaware in March 2007. Alpine Immune Sciences, Inc. (prior to its business combination with Nivalis Therapeutics, Inc.) was incorporated in Delaware on December 30, 2014. The merger is intended to qualify for federal income tax purposes as a tax-free reorganization under the provisions of Section 368(a) of the Internal Revenue Code of 1986, as amended. At the closing of the merger, each outstanding share of our capital stock (common stock and preferred stock) was converted into the right to receive shares of Nivalis common stock (subject to the payment of cash in lieu of fractional shares and after giving effect to a 1:4 reverse stock split of Nivalis common stock) such that, immediately following the effective time of the merger, preexisting Nivalis stockholders, optionholders, and warrantholders owned, or held rights to acquire, approximately 26% of the fully-diluted common stock of Nivalis, which changed its name to “Alpine Immune Sciences, Inc.” following the completion of the merger and Alpine’s preexisting stockholders, optionholders, and warrantholders owned, or held rights to acquire approximately 74% of the fully-diluted common stock of Nivalis. The issuance of the shares to our pre-existing stockholders was registered under the Securities Act of 1933, as amended, pursuant to a registration statement on Form S-4 (No. 333-218134) (the “Registration Statement”) declared effective by the Securities and Exchange Commission (the “SEC”) on June 6, 2017. Contemporaneously with the execution and delivery of the Merger Agreement, certain of our pre-existing stockholders entered into a subscription agreement with us pursuant to which such stockholders purchased, immediately prior to the closing of the merger, 1,335,118 shares of our capital stock at a purchase price of $12.74 per share for an aggregate purchase price of approximately $17.0 million . The merger and the subscription described above were consummated on July 24, 2017 .

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation and Use of Estimates The accompanying consolidated financial statements have been prepared in accordance with the rules and regulations of the SEC and generally accepted accounting principles in the United States of America (“GAAP”). The preparation of financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Significant estimates inherent in the preparation of the accompanying consolidated financial statements include accruals for clinical trial activities and other accruals, and the estimated fair value of equity-based awards. We base our estimates and assumptions on historical experience when available and on various factors we believe to be reasonable under the circumstances. Actual results could differ materially from those estimates. Principles of Consolidation Our consolidated financial statements include the financial position and results of operations of Alpine and our wholly owned operating company and subsidiaries, AIS Operating Co., Inc., and Alpine Immune Sciences Australia PTY LTD. On July 24, 2017 , we closed the merger on the terms described in more detail in Note 1 . In connection with the merger, Nivalis effected a 1:4 reverse stock split of its common stock. Upon the closing of the merger, (1) a wholly-owned subsidiary of Nivalis merged with and into Alpine, with Alpine (renamed as “AIS Operating Co., Inc.”) remaining as the surviving entity; and (2) Nivalis was renamed as “Alpine Immune Sciences, Inc.” Segments We operate as one operating segment and use cash flow as the primary measure to manage our business. Cash and Cash Equivalents and Restricted cash We consider all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash and cash equivalents consist of deposits with commercial banks in checking and interest-bearing accounts, and highly liquid money market funds. Restricted cash represents cash drawn on a line of credit used to establish collateral to support the security deposit on our operating lease to rent office and laboratory space in Seattle, Washington. Periodically, we maintain deposits in financial institutions in excess of government insured limits. We believe we are not exposed to significant credit risk as our deposits, which are held at financial institutions, are high credit quality securities such as money market funds, U.S. Treasury securities, and commercial paper. To date, we have not realized any losses on these deposits. Short-Term Investments Our short-term investments include funds invested in highly liquid money market funds, U.S. Treasury securities, commercial paper, and corporate debt securities with a final maturity of each security of less than one year. All investments are classified as available-for-sale securities and are recorded at fair value based on quoted prices in active markets, with unrealized gains and losses excluded from earnings and reported in other comprehensive income (loss). Purchase premiums and discounts are recognized as interest income using the interest method over the terms of the securities. Realized gains and losses and declines in fair value deemed to be other than temporary are reflected in the Consolidated Statements of Operations and Comprehensive Income (Loss) using the specific-identification method. Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets, generally three to five years, while leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to operations. Maintenance and repairs are expensed as incurred. Major improvements are capitalized as additions to property and equipment. Intangible Asset Our intangible asset is our indefinite-life S-nitrosoglutathione reductase (“GSNOR”) inhibitor in-process research and development asset (“IPR&D”) acquired from Nivalis. The IPR&D represents the processes, expertise, and technology employed in the development of GSNOR inhibitors and Nivalis’ lead product candidate, cavosonstat. The IPR&D represents the estimated fair value as of the acquisition date of substantive in-process projects that have not reached technological feasibility. Impairment of Long-lived Assets We evaluate our long-lived tangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. If the carrying value exceeds the undiscounted future cash flows estimated to result from the use and eventual disposition of the asset, we write down the asset to its estimated fair value. Impairment is assessed by comparing the undiscounted cash flows expected to be generated by the asset to its carrying value. We did not record any impairments in the years ended December 31, 2018 , 2017 and 2016 . Accrued Liabilities As part of the process of preparing our consolidated financial statements, we are required to estimate accruals for professional services and research and development expenses. This process involves reviewing contracts and vendor agreements and communicating with applicable personnel to identify services that have been performed on our behalf. We estimate the level of service performed and the associated cost incurred for the service when we have not yet been invoiced or otherwise notified of the actual cost. We estimate accrued liabilities as of each balance sheet date based on known facts and circumstances. Although we do not expect our estimates to be materially different from amounts actually incurred, if our estimates of the status and timing of services performed differ from the actual status and timing of services performed, we may report amounts that are too high or too low in any particular period. To date, we have not experienced any significant adjustments to our estimates. Leases and Deferred Rent We have entered into lease agreements for office and laboratory space. These leases are classified as operating leases. Rent payments, rent-free periods and rent increases are recognized as rent expense on a straight-line basis over the lease term. The difference between rent expense recognized and rental payments is recorded as deferred rent in the accompanying Consolidated Balance Sheets . Common Stock Warrants We granted common stock warrants to certain non-employee professional advisers. We account for our warrants at fair value, with changes in fair value recognized in operating expenses. Common stock warrants are initially recorded at their issuance date fair value and are subsequently remeasured at each balance sheet date. These warrants are valued using the Black-Scholes option pricing model based on the estimated market value of the underlying common stock at the valuation measurement dates, the remaining contractual term of the warrant, risk-free interest rates, expected dividends, and expected volatility of the price of the underlying common stock. Derivative Financial Instruments We evaluate all of our financial instruments, including issued stock purchase warrants, to determine if such instruments are derivatives or contain features qualifying as embedded derivatives. For derivative financial instruments accounted for as liabilities, the derivative instrument is initially recorded at its fair value and is then re-valued at each reporting date, with changes in the fair value reported in the Consolidated Statements of Operations and Comprehensive Income (Loss) . We use the Black-Scholes option-pricing model to value the derivative instruments at inception and subsequent valuation dates. The classification of derivative instruments, including whether such instruments should be recorded as liabilities or as equity, is re-assessed at the end of each reporting period. We do not use derivative instruments to hedge exposures to cash flow, market, or foreign currency risks. Revenue Recognition (effective January 1, 2018) Revenue is recognized when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Our steps for recognizing revenue consist of; (1) identifying the contract, (2) identifying the performance obligations as either distinct or bundled goods and services, (3) determining the transaction price associated with each performance obligation for which we expect to be entitled in exchange for transferring such goods and services, (4) allocating the transaction price to the performance obligations in the contract and (5) recognizing revenue upon satisfaction of performance obligations. Our collaboration agreements principally contain multiple performance obligations, which may include (1) grants of, or options to obtain, intellectual property licenses; (2) research and development services; and/or (3) manufacturing or supply services. Payments typically received under these arrangements include one or more of the following: non-refundable upfront license fees, option exercise fees, payment for research and/or development efforts, amounts due upon the achievement of specified objectives, and/or royalties on future product sales. Our revenue is primarily derived from our License and Research Agreement (the “Collaboration Agreement”) with Kite Pharma, a Gilead company (“Kite”). See further discussion of the Collaboration Agreement in Note 12 . We allocate revenue to each performance obligation based on its relative stand-alone selling price. We generally determine stand-alone selling prices at the inception of the contract based on our best estimate of what the selling price would be if the deliverable was regularly sold by us on a stand-alone basis. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying Consolidated Balance Sheets and recognized as revenue when the related revenue recognition criteria are met. We recognize revenue under the Collaboration Agreement based on employee hours contributed to each performance obligation. The Collaboration Agreement provides for non-refundable milestone payments. We recognize revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to us for such milestone (1) is consistent with our performance necessary to achieve the milestone or the increase in value to the collaboration resulting from our performance; (2) relates solely to our past performance; and (3) is reasonable relative to all of the other deliverables and payments within the arrangement. In making this assessment, we consider all facts and circumstances relevant to the arrangement, including factors such as the scientific, regulatory, commercial, and other risks that must be overcome to achieve the milestone, the level of effort and investment required to achieve the milestone and whether any portion of the milestone consideration is related to future performance or deliverables. We review the contributed employee hours for each performance obligation under the Collaboration Agreement and adjust the revenue recognized to reflect changes in assumptions relating to the estimated satisfaction of the performance obligation. We could accelerate revenue recognition in the event of early termination of programs or if our expectations change. Alternatively, we could decelerate revenue recognition if programs are extended or delayed. While such changes to our estimates have no impact on our reported cash flows, the timing of revenue recorded in future periods could be materially impacted. See Note 2 included in our Annual Report on Form 10-K for the year ended December 31, 2017 for more discussion regarding the accounting policies that governed revenue recognition prior to January 1, 2018. Research and Development Research and development costs are expensed as incurred. Research and development costs include personnel costs, clinical trials, external contract research and development expenses, raw materials, drug product manufacturing costs and allocated overhead – including depreciation, rent and utilities. Research and development costs that are paid in advance of performance are capitalized as a prepaid expense and amortized over the service period as the services are provided. Stock-based Compensation We account for all stock-based compensation granted to employees and non-employees using a fair value method. Stock-based compensation awarded to employees and non-employees is measured at the grant date fair value for stock option grants. We use the Black-Scholes option pricing model to estimate the fair value of stock options at the grant date. Stock-based compensation to employees is recognized over the requisite service period of the awards, usually the vesting period, on a straight-line basis. Stock-based compensation awarded to non-employees is revalued over its vesting period using a Black-Scholes option pricing model. For performance-based awards where the vesting of the options may be accelerated upon the achievement of certain milestones, vesting and the related stock-based compensation is recognized as an expense when it is probable the milestone will be met. We recognize forfeiture of awards as they occur rather than estimating the expected forfeiture rate. When awards are modified, we compare the fair value of the affected award measured immediately prior to modification to its value after modification. To the extent that the fair value of the modified award exceeds the original award, the incremental fair value of the modified award is recognized as compensation on the date of modification for vested awards, and over the remaining vesting period for unvested awards. Income Taxes Income taxes are accounted for using an asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the consolidated financial statement and tax bases of assets and liabilities at the applicable enacted tax rates. We will establish a valuation allowance for deferred tax assets if it is more likely than not that these items will expire before we are able to realize their benefits or that future deductibility is uncertain. We recognize the tax benefit from uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the tax authorities, based on the technical merits of the position. The tax position is measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. We recognize interest and penalties related to income tax matters in income tax expense if incurred. In December 2017, the SEC issued Staff Accounting Bulletin (“SAB”) 118 to address the application of GAAP in situations in which a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Cuts and Jobs Act (the “Tax Reform Act”) which was signed into law on December 22, 2017. In March 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-05, which amended ASC 740 to incorporate the requirements of SAB 118. We recognized the provisional tax impacts of the Tax Reform Act in the fourth quarter of 2017. Our federal tax loss and research and development credit carryforwards have been updated from the amounts previously provisionally disclosed to reflect a change in position with respect to our 2017 federal research and development credit. The update is a result of additional time spent on modeling the potential use of our tax attributes, as impacted by the Tax Reform Act. Otherwise, during the year ended December 31, 2018, we did not receive any additional information regarding these provisional calculations, except as disclosed in Note 14, Income Taxes . Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net loss and certain changes in equity excluded from net loss. For the years ended December 31, 2018 and 2017 , other comprehensive loss consisted of unrealized losses on our short-term investments. There was no difference between comprehensive loss and net loss for the year ended December 31, 2016. Recently Issued Accounting Pronouncements In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements: Clarifying the Interaction between Topic 808 and Topic 606. This ASU clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue when the collaborative arrangement participant is a customer in the context of a unit of account and precludes recognizing as revenue consideration received from a collaborative arrangement participant if the participant is not a customer. This ASU is effective for public companies for annual reporting periods and interim periods within those annual periods beginning after December 15, 2019. We are currently evaluating the effect, if any, that ASU 2018-18 will have on our consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement. ASU 2018-13 modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. This ASU is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted for any eliminated or modified disclosures. We are evaluating the effect of adopting this new accounting guidance to determine the impact it may have on our financial statements. In June 2018, the FASB issued ASU No. 2018-07, which aligns the measurement and classification guidance for share-based payments to nonemployees with the guidance for share-based payments to employees, with certain exceptions. Under the guidance, the measurement of equity-classified nonemployee awards will be fixed at the grant date. Upon transition, nonemployee awards will be required to be measured at fair value as of the adoption date with a cumulative-effect adjustment recognized in retained earnings as of the beginning of the annual period of adoption. ASU 2018-07 is effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. Early adoption is permitted, but no earlier than an entity’s adoption date of ASC 606. We are evaluating the effect the standard will have on our financial statements and related disclosures. In February 2016, the FASB issued ASU No. 2016-02, Leases. ASU 2016-02 requires a lessee to separate the lease components from the non-lease components in a contract and recognize in the statement of financial position a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. It also aligns lease accounting for lessors with the revenue recognition guidance in ASU 2014-09. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, and is to be applied at the beginning of the earliest period presented using a modified retrospective approach. In July 2018, the FASB issued ASU 2018-11, related to another transition method in lease accounting. If elected, the transition method allows entities to initially apply the new lease standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We plan to adopt ASU 2016-02 on January 1, 2019 and intend to initially apply the new lease standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of the accumulated deficit in the period of adoption as permitted under ASU 2018-11. Based on our leases in place on January 1, 2019 and considering the practical expedients, we expect the adoption of the new standard will not have a material effect on our consolidated statements of operations, will result in a gross-up on our consolidated balance sheets of less than $1.0 million relating to our office and laboratory leases, and will have no effect on our consolidated statements of cash flows. Recently Adopted Accounting Pronouncements Revenue In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, as amended (“new revenue standard” or “ASC 606”), which amends the guidance for revenue recognition to replace numerous industry specific requirements. ASC 606 implements a five-step process for customer contract revenue recognition focusing on transfer of control, as opposed to transfer of risk and rewards. ASC 606 also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Other major provisions include ensuring the time value of money is considered in the transaction price and allowing estimates of variable consideration to be recognized before contingencies are resolved in certain circumstances. ASC 606 is effective for reporting periods beginning after December 15, 2017. On January 1, 2018, we adopted the new accounting standard and all of the related amendments using the modified retrospective method. We recognized the cumulative effect of initially applying the new revenue standard as an adjustment to the opening balance of our accumulated deficit. The cumulative effect of the changes related to the adoption of the new revenue standard increased our beginning balances in accumulated deficit and deferred revenue by $203,000 within our Consolidated Balance Sheets . The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. Our Collaboration Agreement with Kite is the only contract that was impacted by the adoption of the new revenue standard. Prior to the adoption of the new revenue standard, we recognized revenue under the Collaboration Agreement based upon the estimated performance periods related to the non-refundable upfront payments we received from Kite. Under the new standard, we recognize revenue based on employee hours contributed to each performance obligation. In accordance with the new revenue standard requirements, the disclosure of the impact of adoption on our consolidated financial statements as of and for the year ended December 31, 2018 is as follows (in thousands): As Reported Adjustments Balance without Adoption of ASC 606 Consolidated Balance Sheets Stockholders’ equity Accumulated deficit $ (46,074 ) $ (203 ) $ (46,277 ) Consolidated Statements of Operations and Comprehensive Income (Loss) Collaboration revenue $ 705 $ (203 ) $ 502 Net loss (36,487 ) (203 ) (36,690 ) Statement of Cash Flows In August 2016, the FASB issued ASU No. 2016-15 which provides new guidance on the classification of certain cash receipts and payments in the statement of cash flows. The new guidance is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. We adopted this new standard effective January 1, 2018. The adoption of this standard did not impact our financial statements. Share-Based Compensation In May 2017, the FASB issued ASU No. 2017-09 to provide clarity and reduce both diversity in practice and cost and complexity when applying the guidance in Compensation - Stock Compensation (“Topic 718”) about a change to the terms and conditions of a share-based payment award. The amendments in this update provide guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The amendments in this update are effective for annual periods, including interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted and applied prospectively to modifications occurring on or after the adoption date. We adopted this this standard effective January 1, 2018. The adoption of this standard did not have an impact on our financial statements. For the year ended December 31, 2018, there were no modifications to the terms or conditions of a share-based payment award.

Business Combination

Business Combination	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Business Combination	Business Combination On July 24, 2017 , we closed the merger on the terms described in more detail in Note 1 . In connection with the merger, Nivalis effected a 1:4 reverse stock split of its common stock. Upon the closing of the merger, (1) a wholly-owned subsidiary of Nivalis merged with and into Alpine, with Alpine (renamed as “AIS Operating Co., Inc.”) remaining as the surviving entity; and (2) Nivalis was renamed as “Alpine Immune Sciences, Inc.” Under the terms of the Merger Agreement, Nivalis issued shares of its common stock to Alpine’s stockholders, at an exchange rate of 0.4969 shares of Nivalis common stock, after taking into account the 1:4 reverse stock split, for each share of Alpine’s common stock and preferred stock outstanding immediately prior to the merger. The exchange rate was determined through arms-length negotiations between Nivalis and Alpine. Nivalis also assumed all of the stock options outstanding under Alpine’s Amended and Restated 2015 Stock Plan, as amended (the “Alpine Plan”), and stock warrants for Alpine’s capital stock outstanding immediately prior to the merger, with such stock options and warrants henceforth representing the right to purchase a number of shares of the Nivalis common stock equal to 0.4969 multiplied by the number of shares of Alpine’s common stock or preferred stock previously represented by such options and warrants. Nivalis also assumed the Alpine Plan. Immediately after the merger, there were 13,881,645 shares of common stock outstanding. Immediately after the merger, Alpine’s former stockholders, warrantholders, and optionholders owned, or held rights to acquire, approximately 74% of the fully-diluted common stock of Nivalis, which for these purposes is defined as the outstanding common stock of Nivalis, plus “in the money” options and warrants to purchase shares of Nivalis’ common stock, assuming all “in the money” options and warrants of Nivalis outstanding immediately prior to the merger are exercised on a cashless basis immediately prior to the closing of the merger, with Nivalis’ stockholders, optionholders, and warrantholders immediately prior to the merger owning, or holding rights to acquire, approximately 26% of the fully diluted common stock of Nivalis. The issuance of shares of Nivalis’ common stock to our pre-existing stockholders was registered with the SEC pursuant to the Registration Statement. Immediately prior to the merger, we issued and sold an aggregate of approximately $17.0 million of shares of our capital stock to certain existing stockholders. For accounting purposes, our historical financial statements were not adjusted to reflect the merger, other than adjustments to the capital structure to reflect the historical capital structure of Nivalis. No other adjustments to our historical assets and liabilities were made as a result of the merger. In addition to the operating assets and liabilities of Nivalis, we also acquired Nivalis’ tax attributes, which primarily consisted of net operating losses which begin to expire in 2032. Our ability to utilize the tax attributes of Nivalis may be limited under Section 382 of the U.S. Internal Revenue Service and as such, have been reserved. We recorded a deferred tax liability related to future tax benefits arising from IPR&D acquired in the Merger. The combined organization is focusing on the development and commercialization of our innovative immunotherapies. Following the merger, the increased cash resources and increased access to capital of the combined organization will help to support the clinical development of our products. Consideration Transferred The fair value of the consideration transferred was based on the most reliable measure, which was determined to be the market price of Nivalis shares of common stock as of the acquisition date. The fair value of the consideration transferred consisted of the following (in thousands except share and per share amounts): Outstanding Nivalis common stock 3,914,058 Per share fair value of Nivalis common stock $ 9.60 Outstanding Nivalis stock options 421,992 Weighted average per share fair value of Nivalis stock options $ 1.25 Total fair value of consideration (in 000’s) $ 38,103 Pursuant to the Merger Agreement, unvested Nivalis stock options immediately vested as of the closing of the business combination and were adjusted to give effect to the recapitalization. Purchase Price Allocation As Alpine was the accounting acquirer in the merger, we allocated the purchase price to the acquired tangible and intangible assets and assumed liabilities of Nivalis based on their estimated fair values as of the acquisition date. The excess of the estimated fair values of net assets acquired over the acquisition consideration paid was recorded as a bargain purchase gain in the Consolidated Statements of Operations and Comprehensive Income (Loss) . The determination of the fair values of the assets acquired and liabilities assumed requires significant judgment, including third party valuation estimates relating to the value of the acquired IPR&D. The allocation of the purchase consideration to the assets acquired and liabilities assumed in our financial statements was finalized as of December 31, 2017. The final allocation of the purchase consideration is as follows (in thousands): Assets: Fair Value Cash and cash equivalents $ 31,130 Marketable securities 12,952 Other receivables 79 IPR&D 1,453 Total assets acquired 45,614 Liabilities: Accrued liabilities (401 ) Deferred tax liability (509 ) Total liabilities assumed (910 ) Bargain purchase gain (6,601 ) Total $ 38,103 We relied on significant Level 3 unobservable inputs to estimate the fair value of our acquired IPR&D using management’s estimate of future royalties and expected earnings of the assets after taking into account an estimate of future expenses necessary to bring the products to completion. These projected cash flows were then discounted to their present values using a discount rate of 17% , which was considered commensurate with the risks and stages of development of the IPR&D. The bargain purchase gain resulted from expenses incurred by Nivalis between the time the purchase price was negotiated and the close of the transaction, and changes in the Nivalis stock price during that period as the exchange ratio was fixed when the purchase price was negotiated. We recognized acquisition-related costs of $1.5 million for the year ended December 31, 2017. These costs are included within general and administrative expense in our Consolidated Statements of Operations and Comprehensive Income (Loss) . Pro Forma Financial Information The following pro forma consolidated results of net loss for the year ended December 31, 2017 assume the business combination was completed as of January 1, 2017 (in thousands, except per share amounts): Year Ended December 31, 2017 Pro forma revenues $ 1,731 Pro forma net loss (18,327 ) Pro forma basic and diluted net loss per share $ (1.32 ) For purposes of the pro forma disclosures above, the primary adjustments for the year ended December 31, 2017 includes the elimination of acquisition related costs and acceleration of stock compensation expense upon the change in control.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. In 2016, we considered our convertible preferred stock to be participating securities, and we computed net loss per share attributable to common stockholders using the two-class method required for participating securities. All participating securities are excluded from basic weighted-average common shares outstanding. In accordance with the two-class method, earnings allocated to these participating securities, which include participation rights in undistributed earnings, are subtracted from net income to determine total undistributed earnings to be allocated to common stockholders. Net loss is not allocated to participating securities as there is no contractual obligation to share in net losses. The net loss per share for the year ended December 31, 2017 includes the conversion of 9,301,433 shares of our convertible preferred stock into common stock, and 3,914,058 shares acquired in connection with the merger. The significant number of shares issued has affected the year-over-year comparability of our net loss per share calculations. The common stock issuable upon the conversion or exercise of the following dilutive securities has been excluded from the diluted net loss per share attributable to common stockholders calculation because their effect would have been antidilutive. Diluted net loss per share, therefore, does not differ from basic net loss per share for the periods presented: December 31, 2018 2017 2016 Convertible preferred stock — — 4,311,770 Warrants to purchase common stock 24,123 24,123 12,422 Options to purchase common stock 2,509,850 1,611,996 520,739 Total 2,533,973 1,636,119 4,844,931

Cash Equivalents and Short-Term

Cash Equivalents and Short-Term Investments	12 Months Ended
	Dec. 31, 2018
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash Equivalents and Short-term Investments	Cash Equivalents and Short-Term Investments The amortized cost and fair value of our cash equivalents and short-term investments are as follows (in thousands): December 31, 2018 Amortized Gross Gross Fair market Money market funds $ 6,405 $ — $ — $ 6,405 U.S. treasury bills 13,966 — (2 ) 13,964 Corporate debt securities and commercial paper 31,331 — (11 ) 31,320 Total $ 51,702 $ — $ (13 ) $ 51,689 December 31, 2017 Amortized Cost Gross unrealized gains Gross unrealized losses Fair market value Money market funds $ 5,680 $ — $ — $ 5,680 U.S. treasury bills 19,909 — (21 ) 19,888 Corporate debt securities and commercial paper 53,390 — (38 ) 53,352 Total $ 78,979 $ — $ (59 ) $ 78,920 All short-term investments held as of December 31, 2018 and 2017 were classified as available-for-sale securities and had contractual maturities of less than one year . There were no realized gains and losses on these securities for the periods presented.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Cash and cash equivalents, receivables, accounts payable and accrued liabilities, which are recorded at invoiced amount or cost, approximate fair value based on the short-term nature of these financial instruments. Fair value is defined as the exchange price received for an asset or paid to transfer a liability, or 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. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value, is as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 : Unobservable inputs supported by little or no market activity and significant to the fair value of the assets or liabilities. As of December 31, 2018 and 2017 , cash of $614,000 and $2.3 million , respectively, is excluded from the fair value table below. The following table summarizes our financial assets and liabilities measured at fair value on a recurring basis (in thousands): Assets: December 31, 2018 Level 1 Level 2 Level 3 Total Money market funds $ 6,405 $ — $ — $ 6,405 U.S. treasury bills 13,964 — — 13,964 Corporate debt securities and commercial paper — 31,320 — 31,320 Total $ 20,369 $ 31,320 $ — $ 51,689 Assets: December 31, 2017 Level 1 Level 2 Level 3 Total Money market funds $ 5,680 $ — $ — $ 5,680 U.S. treasury bills 19,888 — — 19,888 Corporate debt securities and commercial paper — 53,352 — 53,352 Total $ 25,568 $ 53,352 $ — $ 78,920 Our Level 2 assets consist of commercial paper and corporate debt securities. We review trading activity and pricing for our available-for-sale securities as of the measurement date. When sufficient quoted pricing for identical securities is not available, we use market pricing and other observable market inputs for similar securities obtained from various third-party data providers. These inputs either represent quoted prices for similar assets in active markets or have been derived from observable market data.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and Equipment Property and equipment, net consist of the following (in thousands): December 31, 2018 2017 Laboratory equipment $ 1,506 $ 1,161 General equipment and furniture 158 110 Computer equipment and software 103 82 Leasehold improvements 128 47 Property and equipment, at cost 1,895 1,400 Less accumulated depreciation and amortization (699 ) (311 ) Property and equipment, net $ 1,196 $ 1,089 Depreciation expense was $388,000 , $241,000 and $69,000 for the years ended December 31, 2018 , 2017 and 2016 , respectively.

Loss on Sale of Intangible Asse

Loss on Sale of Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Loss on Sale of Intangible Assets	Loss on Sale of Intangible Asset In February 2018, we entered into an Option License Agreement (“Option Agreement”) with Laurel Venture Capital Ltd. (“Laurel”), which granted Laurel a limited license to evaluate the indefinite-life GSNOR inhibitor IPR&D asset acquired as part of the merger with Nivalis in 2017. The IPR&D represents the processes, expertise, and technology employed in the development of GSNOR inhibitors and Nivalis’ lead product candidate, cavosonstat. Under the Option Agreement, we received an upfront non-refundable payment of $75,000 , which was recognized as revenue in our accompanying Consolidated Statements of Operations and Comprehensive Income (Loss) . In June 2018, we entered into an Asset Purchase Agreement (“Purchase Agreement”) with Laurel and completed the sale of global rights to the GSNOR asset. As consideration under the Purchase Agreement, we received a non-refundable closing payment of $250,000 , which was accounted for as a purchase of our intangible asset. We are also eligible to receive an additional payment of approximately $425,000 on the one-year anniversary of the sale completion date. In addition, we are eligible to receive milestone payments of up to $20.0 million , in the aggregate upon satisfaction by Laurel of certain regulatory approval milestones. We will also be eligible to receive royalty payments equal to a low single-digit percentage rate of worldwide net sales of any approved products. If Laurel transfers any part of the rights to the GSNOR assets within 12 months of the sale completion date, we will be eligible to receive one-fourth of any cash payments made to Laurel by a transferee within 18 months of the sale completion date and such transferee will remain obligated with respect to Laurel’s milestone and royalty obligations to us. Upon the sale of the GSNOR assets, we derecognized the full carrying value of the intangible asset of $1.5 million on our accompanying Consolidated Balance Sheets and recognized a loss on the sale of the intangible asset of $1.2 million on the accompanying Consolidated Statements of Operations and Comprehensive Income (Loss) .

Additional Consolidated Balance

Additional Consolidated Balance Sheets Information	12 Months Ended
	Dec. 31, 2018
Disclosure Text Block Supplement [Abstract]
Additional Consolidated Balance Sheets Information	Additional Consolidated Balance Sheets Information Prepaid expenses and other current assets consists of the following (in thousands): December 31, 2018 2017 Deferred financing costs $ 477 $ — Prepaid insurance 300 298 Prepaid research and development 83 791 Prepaid other 145 91 Other receivables 237 128 Prepaid expenses and other current assets $ 1,242 $ 1,308 Accrued liabilities and other current liabilities consisted of the following (in thousands): December 31, 2018 2017 Research and development services $ 2,457 $ 197 Employee compensation 1,009 4 Legal and professional fees 646 112 Accrued other 165 69 Total $ 4,277 $ 382

Long-term Debt

Long-term Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Long-term Debt	Long-term Debt We maintain a long-term financing arrangement with Silicon Valley Bank. On June 30, 2017, we drew down a term loan of $5.0 million . The loan had an interest-only period that expired on July 1, 2018 , at which point we became obligated to make thirty consecutive equal monthly payments of principal (each in an amount that will fully amortize the loan), plus accrued interest. Interest accrues at a floating per annum rate equal to the lender’s prime rate minus 1.75% . As a condition to the loan, we agreed to pay a final payment fee of 7.5% , or $375,000 , upon repayment of the loan. The final payment fee was recorded in long-term debt with an offsetting reduction in long-term debt and was accounted for as a debt discount. Pursuant to the loan agreement we have pledged substantially all of our assets, excluding intellectual property, as collateral. The obligations under the loan agreement are subject to acceleration upon the occurrence of specified events of default, including a material adverse change in our business, operations, financial, or other condition. We assessed the likelihood of the lender accelerating payment of the loan due to a material adverse change in our business, operations, financial, or other condition as remote. As such, as of December 31, 2018 , the classification of the loan is split between current and noncurrent based on the timing of payment obligations. The term loan agreement contains customary conditions to borrowings, events of default and negative covenants, including covenants that could limit our ability to, among other things, incur additional indebtedness, liens or other encumbrances; make dividends or other distributions; buy, sell or transfer assets; engage in any new line of business; and enter into certain transactions with affiliates. We were in compliance with our covenants as of December 31, 2018 . Also, in connection with the drawdown of the loan, we granted Silicon Valley Bank 7,069 Series A -1 Preferred Stock warrants at an exercise price of $12.38 per share. The fair value of the warrants on the date of issuance was $53,000 , determined using the Black-Scholes option-pricing model, and was recorded as a discount to the note and as a warrant liability on the accompanying Consolidated Balance Sheets . In connection with the merger and conversion of all outstanding Series A-1 preferred stock, the warrants became exercisable for 7,069 fully vested shares of our common stock. As a result of the change in the underlying shares, the warrants were equity-classified beginning on July 24, 2017 . The debt discount is being amortized to interest expense using the effective interest method over the repayment term of the initial loan amount. Non-cash interest expense associated with the amortization of the discount was $169,000 and $87,000 , for years ended December 31, 2018 and 2017 , respectively. The unamortized discount was $172,000 as of December 31, 2018 . Future principal payments as of December 31, 2018 under our loan based on contractual maturities are as follows (in thousands): Year Ending December 31, Total 2019 $ 2,000 2020 2,000 2021 — 2022 — 2023 — Total future principal payments $ 4,000

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Operating Lease In 2016, we entered into a non-cancelable operating lease to rent office and laboratory space in Seattle, Washington. In April 2016, we amended the agreement to lease additional premises adjacent to our existing leased premises. Under our lease agreements, we lease approximately 11,158 square feet of office and laboratory space with an annual base rent of $566,000 in the first year, which will increase by 3% each year thereafter. The leases expire on December 31, 2019 and has two options to extend the lease term with each option enabling us to extend the lease term by twelve months . As required by the terms of the lease, in May 2017, we entered into a line of credit to establish collateral to support the security deposit in an amount of $132,000 . This is recorded as restricted cash in the accompanying Consolidated Balance Sheets . In January 2018, we entered into a lease amendment for approximately 6,184 square feet of additional office and laboratory space adjacent to our existing leased premises in Seattle, Washington. The lease expires on December 31, 2019 and has two options to extend the lease term with each option enabling us to extend the lease term by twelve months . The annual base rent due under the lease is $295,000 for the first year and will increase by 3.0% each year thereafter. We recognize rent expense on a straight-line basis over the lease period and accrue for rent expense incurred but not paid. The lease also requires us to pay additional amounts for operating and maintenance expenses. Rent expense was $811,000 , $529,000 and $267,000 for the years ended December 31, 2018 , 2017 and 2016 , respectively. Future minimum lease payments for our non-cancelable operating leases at December 31, 2018 are as follows (in thousands): Minimum Lease Payments 2019 $ 930 2020 9 2021 9 2022 1 2023 — Total future minimum lease payments $ 949 In March 2019, we entered into a lease with ARE-Seattle No. 28, LLC (the “Landlord”) for 27,164 square feet of office and laboratory space located at 188 East Blaine Street, Seattle, Washington. The term of the lease is 10.8 years with one option to extend the term by 5.0 years . The target “Commencement Date” is May 1, 2019 and shall be the date that Landlord delivers the premises to us in substantially complete condition. The “Rent Commencement Date” shall be the date that is nine months after the Commencement Date. The annual base rent due under the lease is $1.7 million for the first year and will increase by 3.0% each year thereafter. We will not be required to pay base rent from the Rent Commencement Date through the last day of the ninth month following the Rent Commencement Date. We will receive a maximum tenant improvement allowance of $5.4 million , which is included in our base rent, and a maximum additional tenant improvement allowance of $1.8 million , which will result in additional rent amortized over the term of the lease at an annual rate of 8.0% . The lease also requires us to pay additional amounts for operating and maintenance expenses. In connection with the lease, we provided a $254,000 letter of credit as a security deposit. Rent payments under our lease with ARE are not included in the table above.

Collaboration and License Agree

Collaboration and License Agreement	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration and License Agreement	Collaboration and License Agreement In October 2015, we entered into a Collaboration Agreement with Kite to discover and develop protein-based immunotherapies targeting the immune synapse to treat cancer. Under our agreement, we are to perform certain research services and grant to Kite an exclusive license to two programs from our transmembrane immunomodulatory protein (“TIP”) technology, which Kite is planning to further engineer into chimeric antigen receptor (“CAR”) and T cell receptor (“TCR”) product candidates. Under the terms of the Collaboration Agreement, in 2015, Kite made upfront payments to us of $5.5 million , which were initially recorded as deferred revenue. As of December 31, 2018 , we are also eligible to receive milestone payments based upon the successful achievement of pre-specified research, clinical, and regulatory milestones totaling up to $530.0 million plus royalty payments on product sales, if any. Kite will receive an exclusive, worldwide license to research, develop, and commercialize engineered autologous T cell therapies incorporating two programs coming from our platform. In October 2017, we entered into an amendment with Kite to extend the research term of the Collaboration Agreement. Under the amended agreement, we became eligible to receive an additional $450,000 in research support payments from Kite in two tranches. In June 2018, we recognized one of the research support payments under the amended agreement. In October 2018, we entered into another amendment with Kite, which amended portions of the research plan. We have recorded revenue of $630,000 , $1.7 million and $2.9 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, under the Collaboration and Licensing Agreement. In the second quarter of 2018, based on the completion of our research and development efforts in connection with the performance period, we recognized the remaining balance in deferred revenue on our accompanying Consolidated Balance Sheets . As further discussed in Note 2 , on January 1, 2018, we adopted the new revenue standard using the modified retrospective method. Prior to the adoption of the new revenue standard, we recognized revenue under the Collaboration Agreement based upon the estimated performance periods related to the non-refundable upfront payments we received from Kite. Under the new standard, we recognize revenue based on employee hours contributed to each performance obligation. We recognized $203,000 in higher revenue for the year ended December 31, 2018, as compared to what would have been recorded under previous accounting guidance.

Stockholders' Deficit

Stockholders' Deficit	12 Months Ended
	Dec. 31, 2018
Stockholders' Equity Note [Abstract]
Stockholders’ Deficit	Stockholders’ Deficit Common Stock Upon the closing of the merger in 2017, all outstanding shares of our convertible preferred stock converted into 9,301,433 shares of common stock. As of December 31, 2018 and 2017 , we did not have any convertible preferred stock outstanding. We had 13,854,205 and 13,831,178 shares of common stock outstanding as of December 31, 2018 and 2017 , respectively. Shares of common stock reserved for future issuance were as follows: December 31, 2018 2017 Shares to be issued upon exercise of outstanding stock options 2,509,850 1,611,996 Shares to be issued upon conversion of common stock warrants 24,123 24,123 Shares available for future stock grants 496,530 576,722 Shares to be issued under employee stock purchase plan 45,211 45,211 Shares of common stock reserved for future issuance 3,075,714 2,258,052 In December 2017, we repurchased 50,467 shares of unvested common stock issued to one of our former employees for the original purchase price of $0.002 per share. Securities Offerings In July 2016, we entered into a sales agreement (the “Cowen Sales Agreement”) with Cowen and Company, LLC (“Cowen”) to sell shares of our common stock having aggregate sales proceeds of up to $30.0 million , from time to time, through an “at the market” equity offering program under which Cowen acted as our sales agent. In June 2018, we and Cowen agreed to terminate the Cowen Sales Agreement. In June 2018, we entered into an equity distribution agreement, (“Equity Distribution Agreement”), with Piper Jaffray & Co., (“Piper Jaffray”), pursuant to which we may sell shares of our common stock through an “at the market” equity offering program for up to $50.0 million , in gross cash proceeds. Piper Jaffray will be entitled to compensation for its services of up to 3.0% of the gross sales price per share of all shares sold through Piper Jaffray under the Equity Distribution Agreement. The Equity Distribution Agreement may be terminated by us upon written notice to Piper Jaffray for any reason or by Piper Jaffray upon written notice to us for any reason or at any time under certain circumstances, including but not limited to if we experience a material adverse change. Under the Equity Distribution Agreement, we will set the parameters for the sale of shares, including the number of shares to be issued, the time period during which sales are requested to be made, limitation on the number of shares that may be sold in any one trading day and any minimum price below which sales may not be made. We have no obligation to sell any shares under the Equity Distribution Agreement and may at any time suspend solicitation and offers under the Equity Distribution Agreement. The shares will be issued pursuant to our effective shelf registration statement on Form S-3 (File No. 333-212404), declared effective by the SEC on July 14, 2016. We filed a prospectus supplement (the “Prospectus Supplement”), dated June 11, 2018, with the SEC in connection with the offer and sale of the shares pursuant to the Equity Distribution Agreement. The Prospectus Supplement relates to the offering of $14.5 million in shares of our common stock and we will be required to file an additional prospectus supplement in the event we seek to offer more than $14.5 million in shares of our common stock in accordance with the Equity Distribution Agreement. As December 31, 2018 , we have made no sales under the Equity Distribution Agreement. In January 2019, we entered into a securities purchase agreement (the “Purchase Agreement”) with a limited number of accredited investors, pursuant to which we, in a private placement (the “Private Placement”), sold $25.3 million units (the “Units”) for a purchase price of $5.37 per Unit. Each Unit consists of one share of our common stock and a warrant to purchase 0.39 shares of common stock. Pursuant to the terms of the Purchase Agreement, we issued 4,706,700 shares of common stock and warrants to purchase an aggregate of 1,835,610 shares of common stock. The warrants have an exercise price of $12.74 and have a term of five years . The securities being sold in the Private Placement have not been registered under the Securities Act of 1933, as amended, or state securities laws and may not be offered or sold in the United States absent registration with the SEC or an applicable exemption from such registration requirements. We have agreed to file a registration statement with the SEC covering the resale of the shares of common stock issuable in connection with the Private Placement and upon exercise of the warrants. We have incurred legal, accounting and other direct costs related to our efforts to raise capital. These costs have been capitalized as deferred financing costs and are included within prepaid expenses and other current assets in our accompanying Consolidated Balance Sheets . These costs are deferred until completion of an offering, at which time they will be reclassified to additional paid-in capital as a reduction of the proceeds. As December 31, 2018 , we have incurred $477,000 of deferred financing costs. Common Stock Warrants We have issued warrants in connection with the drawdown of our SVB loan, and to certain non-employee professional advisers. We also assumed warrants in connection with the merger. No additional warrants were issued or exercised during the year ended December 31, 2018. A summary of our warrant activity is presented below: Warrants Outstanding Weighted- average Exercise Price Weighted- average Remaining Contract Term (in years) Outstanding at December 31, 2017 24,123 $ 24.86 6.62 Outstanding at December 31, 2018 24,123 $ 24.86 5.62 Exercisable at December 31, 2018 17,153 $ 32.92 5.76 Equity Incentive Plans In April 2018, our board of directors adopted, and in June 2018 our stockholders approved, the 2018 Equity Incentive Plan (“2018 Plan”) under which 901,530 shares of our common stock were initially reserved for issuance, and we ceased granting stock awards under the Nivalis Therapeutics, Inc. 2015 Equity Incentive Plan (the “2015 EIP”) and the Amended and Restated 2015 Stock Plan (the “2015 Plan”), collectively, the “Legacy Plans”. All shares of common stock subject to awards under the Legacy Plans that expire or terminate without having been exercised in full, or are forfeited to or repurchased by the company, will be added to the 2018 Plan up to a maximum of 1,972,784 shares. Additionally, our 2018 Plan provides for an annual increase in the number of shares reserved for insurance under our 2018 Plan equal to the lesser of (1) 5% of the number of shares of common stock outstanding as of the last day of the preceding calendar year and (2) 1,500,000 . However, our board of directors may act prior to January 1 of a given year to provide that there will be no January 1 increase for such year or that the increase for such year will be a lesser number of shares. On January 1, 2019, a total of 692,710 additional shares were automatically added to the shares authorized under the 2018 Plan. In August 2018 our board of directors approved an “inducement” option grant, pursuant to Rule 5635(c)(4) of the Nasdaq Listing Rules, to purchase 150,000 shares of our common stock to our President and Chief Operating Officer. The option grant was exempt from registration under the Securities Act of 1933, as amended, pursuant to Section 4(a)(2) thereof as a transaction by an issuer not involving a public offering. The options granted vest within four years, subject to continued employment, and expire ten years after the date of grant. In July 2017, in connection with the merger, we assumed Nivalis’ Employee Stock Purchase Plan (the “ESPP”) and the 2015 EIP. Upon assumption of the ESPP, there were 45,211 shares available for issuance under the ESPP. As of December 31, 2018 , we have not activated the ESPP. Stock options granted under our equity plans generally vest within four years and vested options are exercisable from the grant date until ten years after the date of grant. Vesting of certain employee options may be accelerated in the event of a change in control of the Company. We grant stock options to employees with exercise prices equal to the fair value of our common stock on the date of grant. The term of incentive stock options may not exceed ten years from the date of grant. We utilize newly issued shares to satisfy option exercises. As of December 31, 2018, a total of 3,061,084 shares of common stock were authorized for issuance under our 2018 Plan, 2015 Plan and 2015 EIP, and 496,530 shares were available for future grants under our 2018 Plan. A summary of stock option activity under our plans is presented below: Options Outstanding Weighted- average Exercise Price Weighted- average Remaining Contract Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2017 1,611,996 $ 4.32 Granted 936,750 $ 8.34 Exercised (23,027 ) $ 0.39 Forfeited/Expired (15,869 ) $ 10.01 Outstanding at December 31, 2018 2,509,850 $ 5.82 8.11 $ 2,548 Vested and expected to vest after December 31, 2018 2,484,850 $ 5.81 8.10 $ 2,548 Exercisable at December 31, 2018 887,134 $ 4.26 6.66 $ 1,535 As of December 31, 2018 , there was $6.5 million of unrecognized stock-based compensation expense related to nonvested stock options that is expected to be recognized over a weighted-average period of 2.9 years . The aggregate intrinsic value of stock options exercised during the year ended December 31, 2018 , 2017 and 2016 was $214,000 , $18,000 and $22,000 . The total fair value of shares vested during the years ended December 31, 2018 , 2017 and 2016 was $1.8 million , $139,000 and $70,000 , respectively. Stock-Based Compensation Expense We use the Black-Scholes option pricing model to estimate the fair value of stock options at the grant date. The Black-Scholes option pricing model requires us to make certain estimates and assumptions, including assumptions related to the expected price volatility of our stock, the period during which the options will be outstanding, the rate of return on risk-free investments, and the expected dividend yield of our stock. The fair values of stock options granted to employees were calculated using the following assumptions: Years Ended December 31, 2018 2017 2016 Weighted-average estimated fair value at grant $5.43 $4.69 $0.42 Risk-free interest rate (1) 2.27% - 3.07% 1.90% - 2.26% 1.14% - 2.24% Expected term of options (in years) (2) 5.50 – 7.00 5.69 – 6.32 5.22 – 7.00 Expected stock price volatility (3) 70% - 77% 72% - 83% 72% - 79% Expected dividend yield (4) —% —% —% (1) The risk-free interest rate assumption was based on zero-coupon U.S. Treasury instruments that had terms consistent with the expected term of our stock option grants. (2) We used the “simplified method” for options to determine the expected term of stock option granted to employees, since we do not have sufficient historical exercise data to provide a reasonable basis upon which to estimate expected term due to the limited time our shares have been publicly traded. Under this approach, the weighted-average expected life is presumed to be the average of the vesting term and the contractual term of the option. (3) Volatility is a measure of the amount by which a financial variable, such as share price, has fluctuated or is expected to fluctuate during a period. We analyzed the stock price volatility of companies at a similar stage of development to estimate expected volatility of our stock price. (4) We have never declared or paid any cash dividends and do not presently plan to pay cash dividends in the foreseeable future. The fair value of each non-employee stock option is estimated at the date of grant using the Black-Scholes option pricing model is are remeasured over the vesting term, as earned. Assumptions used in valuing non-employee stock options are generally consistent with those used for employee stock options, with the exception that the expected term is over the contractual life of the option. Stock-based compensation expense is classified in the Consolidated Statements of Operations and Comprehensive Income (Loss) as follows (in thousands): Years Ended December 31, 2018 2017 2016 Employee: Research and development $ 890 $ 183 $ 14 General and administrative 1,385 588 53 Non-Employee: Research and development 16 52 5 General and administrative 18 15 5 Total stock-based compensation expense $ 2,309 $ 838 $ 77 In May 2016 we extended the vesting period of 567,500 unvested share options held by five employees. As a result of this modification, we recognized additional compensation expense of $4,000 for the year ended December 31, 2016.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes On December 22, 2017, the U.S. government enacted the Tax Act. The Tax Act incorporates broad and complex changes to the U.S. tax code. The main provision of the Tax Act that is applicable to us is the reduction of a maximum federal tax rate of 35% to a flat tax rate of 21%, effective January 1, 2018. We incorporated the change in federal tax rates in our annual tax provision for the annual period ended December 31, 2017. Additionally, SAB 118 was issued to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Act. December 22, 2018 marked the end of the measurement period for purposes of SAB 118. We have completed and recorded the adjustments necessary under SAB 118 related to the Tax Act. Our income (loss) before taxes is derived from domestic (United States) sources. The provision for income taxes is composed of the following (in thousands): Years Ended December 31, 2018 2017 Current: U.S. - Federal $ — $ (1 ) U.S. - State (61 ) 5 Total current (61 ) 4 Deferred: U.S. - Federal (305 ) (204 ) U.S. - State — — Total deferred (305 ) (204 ) Total income tax benefit $ (366 ) $ (200 ) The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows: Years Ended December 31, 2018 2017 U.S. Statutory rate 21.0 % 35.0 % Effect of: State taxes (net of federal benefit) 3.8 % (1.6 )% Permanent differences — % (0.1 )% Federal research and development credit 4.2 % 4.4 % Change in valuation allowance (27.3 )% (19.4 )% Benefit of a lower tax rate (0.1 )% 0.2 % Stock-based compensation (0.6 )% (2.6 )% Non-deductible merger costs — % (17.6 )% Bargain purchase gain — % 28.9 % Tax rate change — % (24.7 )% Effective income tax rate 1.0 % 2.5 % We recorded tax benefits of $366,000 and of $200,000 for the years ended December 31, 2018 and 2017, respectively, which represent effective tax rates of 1.0% and 2.5% for the years ended December 31, 2018 and 2017, respectively. The difference between the U.S. federal statutory tax rates of 21% and 35% and our effective tax rate in all periods is primarily due to a full valuation allowance related to our deferred tax assets, the generation and consumption of federal R&D tax credits, as well as a refund of state taxes from a carryback of the 2018 net operating loss. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The following table represents the significant components of our deferred tax assets and liabilities for the periods presented (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss $ 10,546 $ 2,475 Research and development credits 1,958 458 Intangible asset basis 54 — Deferred revenue — 58 Deferred rent 21 24 Stock based compensation 1,382 810 Other 3 12 Gross deferred tax assets 13,964 3,837 Valuation allowance (13,774 ) (3,722 ) Total deferred tax assets, net of valuation allowance 190 115 Deferred tax liabilities: Prepaid expenses (91 ) (63 ) Fixed asset basis (99 ) (110 ) Intangible asset basis — (247 ) Total deferred tax liability (190 ) (420 ) Net deferred tax assets and liabilities $ — $ (305 ) As part of the merger with Nivalis, we identified $1.5 million of acquired IPR&D. IPR&D acquired in a business combination is an indefinite-lived intangible asset until the completion or abandonment of the associated R&D efforts. As of December 31, 2017, future reversal of the deferred tax liability resulting from IPR&D costs could not be scheduled for tax purposes and therefore could not be considered as a source of future taxable income. A deferred tax liability of $305,000 was recorded in 2017 as a result of the acquired IPR&D having a financial reporting basis of $1.5 million and a tax basis of zero . In the year ended December 31, 2018, we sold the IPR&D and reversed the deferred tax liability. A valuation allowance is provided for deferred tax assets where the recoverability of the assets is uncertain. The determination to provide a valuation allowance is dependent upon the assessment of whether it is more likely than not that sufficient taxable income will be generated to utilize the deferred tax assets. Based on the weight of the available evidence, which includes our historical operating losses, uncertainty of future taxable income, and the accumulated deficit, we provided a full valuation allowance against our deferred tax assets. The valuation allowance increased by $10.0 million and $2.9 million during the year ended December 31, 2018 and December 31, 2017, respectively. We have net operating loss carryforwards as follows (in thousands): December 31, 2018 2017 Federal (before January 1, 2018) $ 11,094 $ 11,784 Federal (after January 1, 2018) $ 33,417 State $ 16,756 $ — Federal and state net operating loss carryforwards created before January 1, 2018 begin to expire in 2037. Federal net operating loss carryforwards created after January 1, 2018 carryforward indefinitely. The State net operating loss carryforwards begin to expire in 2038. We have net research and development tax credit carryforwards as follows (in thousands): December 31, 2018 2017 Federal $ 2,456 $ 458 Federal research and development tax credit carryforwards begin to expire in 2035. Current tax laws impose substantial restrictions on the utilization of R&D credit and net operating loss carryforwards in the event of an ownership change, as defined by the Internal Revenue Code Section 382 and 383. Such an event may limit our ability to utilize net operating losses and R&D tax credit carryforwards. Under Internal Revenue Code Section 382 and 383, the 2017 merger with Nivalis is likely considered an ownership change with respect to the potential limitation of the Nivalis federal tax credits and net operating losses. As such, it is likely that any future utilization of Nivalis federal tax credits and net operating losses is substantially limited. Therefore, as of December 31, 2018, all Nivalis tax credit and net operating loss carryforwards have been reduced to zero . We account for uncertainty in income taxes in accordance with ASC 740. Tax positions are evaluated in a two-step process, whereby we first determine whether it is more likely than not that a tax position will be sustained upon examination by the tax authority, including resolutions of any related appeals or litigation processes, based on technical merit. If a tax position meets the more-likely-than-not recognition threshold it is then measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. The following table summarized the activity related to unrecognized tax benefits (in thousands): December 31, 2018 2017 Unrecognized benefits – beginning of year $ 114 $ 34 Gross increases (decreases) – prior year tax positions 59 (4 ) Gross increases – current year tax positions 296 84 Unrecognized benefit – end of year $ 469 $ 114 All of the unrecognized tax benefits as of December 31, 2018 are accounted for as a reduction in our deferred tax assets. Due to our valuation allowance, none of the $469,000 of unrecognized tax benefits would affect our effective tax rate, if recognized. We do not believe it is reasonably possible that our unrecognized tax benefits will significantly change in the next twelve months. We recognize interest and penalties related to unrecognized tax benefits as income tax expense. There were no accrued interest or penalties related to unrecognized tax benefits for 2018 and 2017. We do not expect any significant change in our unrecognized tax benefits during the next twelve months. Our material income tax jurisdictions are the United States (federal), and California (state). We are subject to audit for tax years 2012 and forward for federal purposes, and 2015 and forward for California.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions In January 2019, in connection with our Purchase Agreement we sold an aggregate of 935,753 shares of common stock and issued warrants to purchase an aggregate of 364,943 shares of common stock for gross proceeds of approximately $5.0 million to certain of our 5% stockholders. See Part III, Item 13 of this Form 10-K for additional information. We have a shared services agreement with Alpine BioVentures GP, LLC, pursuant to which we incurred costs of $0 , $0 and $17,000 for years ended December 31, 2018 , 2017 and 2016 , respectively. We had an accrual of $5,000 related to the shared services agreement at December 31, 2016, which was paid in April 2017.

401(k) Retirement Plan

401(k) Retirement Plan	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
401(k) Retirement Plan	401(k) Retirement Plan We have adopted a 401(k) plan. All employees are eligible to participate, provided they meet the requirements of the plan. To date, we have not matched employee contributions to the plan.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The accompanying consolidated financial statements have been prepared in accordance with the rules and regulations of the SEC and generally accepted accounting principles in the United States of America (“GAAP”). The preparation of financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Significant estimates inherent in the preparation of the accompanying consolidated financial statements include accruals for clinical trial activities and other accruals, and the estimated fair value of equity-based awards. We base our estimates and assumptions on historical experience when available and on various factors we believe to be reasonable under the circumstances. Actual results could differ materially from those estimates.
Principles of Consolidation	Principles of Consolidation Our consolidated financial statements include the financial position and results of operations of Alpine and our wholly owned operating company and subsidiaries, AIS Operating Co., Inc., and Alpine Immune Sciences Australia PTY LTD. On July 24, 2017 , we closed the merger on the terms described in more detail in Note 1 . In connection with the merger, Nivalis effected a 1:4 reverse stock split of its common stock. Upon the closing of the merger, (1) a wholly-owned subsidiary of Nivalis merged with and into Alpine, with Alpine (renamed as “AIS Operating Co., Inc.”) remaining as the surviving entity; and (2) Nivalis was renamed as “Alpine Immune Sciences, Inc.”
Segments	Segments We operate as one operating segment and use cash flow as the primary measure to manage our business.
Cash and Cash Equivalents and Restricted cash	Cash and Cash Equivalents and Restricted cash We consider all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash and cash equivalents consist of deposits with commercial banks in checking and interest-bearing accounts, and highly liquid money market funds. Restricted cash represents cash drawn on a line of credit used to establish collateral to support the security deposit on our operating lease to rent office and laboratory space in Seattle, Washington.
Concentration of Credit Risk	Periodically, we maintain deposits in financial institutions in excess of government insured limits. We believe we are not exposed to significant credit risk as our deposits, which are held at financial institutions, are high credit quality securities such as money market funds, U.S. Treasury securities, and commercial paper. To date, we have not realized any losses on these deposits.
Short-Term Investments	Short-Term Investments Our short-term investments include funds invested in highly liquid money market funds, U.S. Treasury securities, commercial paper, and corporate debt securities with a final maturity of each security of less than one year. All investments are classified as available-for-sale securities and are recorded at fair value based on quoted prices in active markets, with unrealized gains and losses excluded from earnings and reported in other comprehensive income (loss). Purchase premiums and discounts are recognized as interest income using the interest method over the terms of the securities. Realized gains and losses and declines in fair value deemed to be other than temporary are reflected in the Consolidated Statements of Operations and Comprehensive Income (Loss) using the specific-identification method.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets, generally three to five years, while leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to operations. Maintenance and repairs are expensed as incurred. Major improvements are capitalized as additions to property and equipment.
Intangible Asset	Intangible Asset Our intangible asset is our indefinite-life S-nitrosoglutathione reductase (“GSNOR”) inhibitor in-process research and development asset (“IPR&D”) acquired from Nivalis. The IPR&D represents the processes, expertise, and technology employed in the development of GSNOR inhibitors and Nivalis’ lead product candidate, cavosonstat. The IPR&D represents the estimated fair value as of the acquisition date of substantive in-process projects that have not reached technological feasibility.
Impairment of Long-Lived Assets	Impairment of Long-lived Assets We evaluate our long-lived tangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. If the carrying value exceeds the undiscounted future cash flows estimated to result from the use and eventual disposition of the asset, we write down the asset to its estimated fair value. Impairment is assessed by comparing the undiscounted cash flows expected to be generated by the asset to its carrying value. We did not record any impairments in the years ended December 31, 2018 , 2017 and 2016 .
Accrued Liabilities	Accrued Liabilities As part of the process of preparing our consolidated financial statements, we are required to estimate accruals for professional services and research and development expenses. This process involves reviewing contracts and vendor agreements and communicating with applicable personnel to identify services that have been performed on our behalf. We estimate the level of service performed and the associated cost incurred for the service when we have not yet been invoiced or otherwise notified of the actual cost. We estimate accrued liabilities as of each balance sheet date based on known facts and circumstances. Although we do not expect our estimates to be materially different from amounts actually incurred, if our estimates of the status and timing of services performed differ from the actual status and timing of services performed, we may report amounts that are too high or too low in any particular period. To date, we have not experienced any significant adjustments to our estimates.
Leases and Deferred Rent	Leases and Deferred Rent We have entered into lease agreements for office and laboratory space. These leases are classified as operating leases. Rent payments, rent-free periods and rent increases are recognized as rent expense on a straight-line basis over the lease term. The difference between rent expense recognized and rental payments is recorded as deferred rent in the accompanying Consolidated Balance Sheets .
Common Stock Warrants	Common Stock Warrants We granted common stock warrants to certain non-employee professional advisers. We account for our warrants at fair value, with changes in fair value recognized in operating expenses. Common stock warrants are initially recorded at their issuance date fair value and are subsequently remeasured at each balance sheet date. These warrants are valued using the Black-Scholes option pricing model based on the estimated market value of the underlying common stock at the valuation measurement dates, the remaining contractual term of the warrant, risk-free interest rates, expected dividends, and expected volatility of the price of the underlying common stock.
Derivative Financial Instruments	Derivative Financial Instruments We evaluate all of our financial instruments, including issued stock purchase warrants, to determine if such instruments are derivatives or contain features qualifying as embedded derivatives. For derivative financial instruments accounted for as liabilities, the derivative instrument is initially recorded at its fair value and is then re-valued at each reporting date, with changes in the fair value reported in the Consolidated Statements of Operations and Comprehensive Income (Loss) . We use the Black-Scholes option-pricing model to value the derivative instruments at inception and subsequent valuation dates. The classification of derivative instruments, including whether such instruments should be recorded as liabilities or as equity, is re-assessed at the end of each reporting period. We do not use derivative instruments to hedge exposures to cash flow, market, or foreign currency risks.
Revenue Recognition	Revenue Recognition (effective January 1, 2018) Revenue is recognized when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Our steps for recognizing revenue consist of; (1) identifying the contract, (2) identifying the performance obligations as either distinct or bundled goods and services, (3) determining the transaction price associated with each performance obligation for which we expect to be entitled in exchange for transferring such goods and services, (4) allocating the transaction price to the performance obligations in the contract and (5) recognizing revenue upon satisfaction of performance obligations. Our collaboration agreements principally contain multiple performance obligations, which may include (1) grants of, or options to obtain, intellectual property licenses; (2) research and development services; and/or (3) manufacturing or supply services. Payments typically received under these arrangements include one or more of the following: non-refundable upfront license fees, option exercise fees, payment for research and/or development efforts, amounts due upon the achievement of specified objectives, and/or royalties on future product sales. Our revenue is primarily derived from our License and Research Agreement (the “Collaboration Agreement”) with Kite Pharma, a Gilead company (“Kite”). See further discussion of the Collaboration Agreement in Note 12 . We allocate revenue to each performance obligation based on its relative stand-alone selling price. We generally determine stand-alone selling prices at the inception of the contract based on our best estimate of what the selling price would be if the deliverable was regularly sold by us on a stand-alone basis. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying Consolidated Balance Sheets and recognized as revenue when the related revenue recognition criteria are met. We recognize revenue under the Collaboration Agreement based on employee hours contributed to each performance obligation. The Collaboration Agreement provides for non-refundable milestone payments. We recognize revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to us for such milestone (1) is consistent with our performance necessary to achieve the milestone or the increase in value to the collaboration resulting from our performance; (2) relates solely to our past performance; and (3) is reasonable relative to all of the other deliverables and payments within the arrangement. In making this assessment, we consider all facts and circumstances relevant to the arrangement, including factors such as the scientific, regulatory, commercial, and other risks that must be overcome to achieve the milestone, the level of effort and investment required to achieve the milestone and whether any portion of the milestone consideration is related to future performance or deliverables. We review the contributed employee hours for each performance obligation under the Collaboration Agreement and adjust the revenue recognized to reflect changes in assumptions relating to the estimated satisfaction of the performance obligation. We could accelerate revenue recognition in the event of early termination of programs or if our expectations change. Alternatively, we could decelerate revenue recognition if programs are extended or delayed. While such changes to our estimates have no impact on our reported cash flows, the timing of revenue recorded in future periods could be materially impacted.
Research and Development	Research and Development Research and development costs are expensed as incurred. Research and development costs include personnel costs, clinical trials, external contract research and development expenses, raw materials, drug product manufacturing costs and allocated overhead – including depreciation, rent and utilities. Research and development costs that are paid in advance of performance are capitalized as a prepaid expense and amortized over the service period as the services are provided.
Stock-based Compensation	Stock-based Compensation We account for all stock-based compensation granted to employees and non-employees using a fair value method. Stock-based compensation awarded to employees and non-employees is measured at the grant date fair value for stock option grants. We use the Black-Scholes option pricing model to estimate the fair value of stock options at the grant date. Stock-based compensation to employees is recognized over the requisite service period of the awards, usually the vesting period, on a straight-line basis. Stock-based compensation awarded to non-employees is revalued over its vesting period using a Black-Scholes option pricing model. For performance-based awards where the vesting of the options may be accelerated upon the achievement of certain milestones, vesting and the related stock-based compensation is recognized as an expense when it is probable the milestone will be met. We recognize forfeiture of awards as they occur rather than estimating the expected forfeiture rate. When awards are modified, we compare the fair value of the affected award measured immediately prior to modification to its value after modification. To the extent that the fair value of the modified award exceeds the original award, the incremental fair value of the modified award is recognized as compensation on the date of modification for vested awards, and over the remaining vesting period for unvested awards.
Income Taxes	Income Taxes Income taxes are accounted for using an asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the consolidated financial statement and tax bases of assets and liabilities at the applicable enacted tax rates. We will establish a valuation allowance for deferred tax assets if it is more likely than not that these items will expire before we are able to realize their benefits or that future deductibility is uncertain. We recognize the tax benefit from uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the tax authorities, based on the technical merits of the position. The tax position is measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. We recognize interest and penalties related to income tax matters in income tax expense if incurred. In December 2017, the SEC issued Staff Accounting Bulletin (“SAB”) 118 to address the application of GAAP in situations in which a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Cuts and Jobs Act (the “Tax Reform Act”) which was signed into law on December 22, 2017. In March 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-05, which amended ASC 740 to incorporate the requirements of SAB 118. We recognized the provisional tax impacts of the Tax Reform Act in the fourth quarter of 2017. Our federal tax loss and research and development credit carryforwards have been updated from the amounts previously provisionally disclosed to reflect a change in position with respect to our 2017 federal research and development credit. The update is a result of additional time spent on modeling the potential use of our tax attributes, as impacted by the Tax Reform Act. Otherwise, during the year ended December 31, 2018, we did not receive any additional information regarding these provisional calculations, except as disclosed in Note 14, Income Taxes .
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net loss and certain changes in equity excluded from net loss. For the years ended December 31, 2018 and 2017 , other comprehensive loss consisted of unrealized losses on our short-term investments. There was no difference between comprehensive loss and net loss for the year ended December 31, 2016.
Recently Issued and Adopted Accounting Pronouncements	Recently Issued Accounting Pronouncements In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements: Clarifying the Interaction between Topic 808 and Topic 606. This ASU clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue when the collaborative arrangement participant is a customer in the context of a unit of account and precludes recognizing as revenue consideration received from a collaborative arrangement participant if the participant is not a customer. This ASU is effective for public companies for annual reporting periods and interim periods within those annual periods beginning after December 15, 2019. We are currently evaluating the effect, if any, that ASU 2018-18 will have on our consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement. ASU 2018-13 modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. This ASU is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted for any eliminated or modified disclosures. We are evaluating the effect of adopting this new accounting guidance to determine the impact it may have on our financial statements. In June 2018, the FASB issued ASU No. 2018-07, which aligns the measurement and classification guidance for share-based payments to nonemployees with the guidance for share-based payments to employees, with certain exceptions. Under the guidance, the measurement of equity-classified nonemployee awards will be fixed at the grant date. Upon transition, nonemployee awards will be required to be measured at fair value as of the adoption date with a cumulative-effect adjustment recognized in retained earnings as of the beginning of the annual period of adoption. ASU 2018-07 is effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. Early adoption is permitted, but no earlier than an entity’s adoption date of ASC 606. We are evaluating the effect the standard will have on our financial statements and related disclosures. In February 2016, the FASB issued ASU No. 2016-02, Leases. ASU 2016-02 requires a lessee to separate the lease components from the non-lease components in a contract and recognize in the statement of financial position a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. It also aligns lease accounting for lessors with the revenue recognition guidance in ASU 2014-09. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, and is to be applied at the beginning of the earliest period presented using a modified retrospective approach. In July 2018, the FASB issued ASU 2018-11, related to another transition method in lease accounting. If elected, the transition method allows entities to initially apply the new lease standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We plan to adopt ASU 2016-02 on January 1, 2019 and intend to initially apply the new lease standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of the accumulated deficit in the period of adoption as permitted under ASU 2018-11. Based on our leases in place on January 1, 2019 and considering the practical expedients, we expect the adoption of the new standard will not have a material effect on our consolidated statements of operations, will result in a gross-up on our consolidated balance sheets of less than $1.0 million relating to our office and laboratory leases, and will have no effect on our consolidated statements of cash flows. Recently Adopted Accounting Pronouncements Revenue In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, as amended (“new revenue standard” or “ASC 606”), which amends the guidance for revenue recognition to replace numerous industry specific requirements. ASC 606 implements a five-step process for customer contract revenue recognition focusing on transfer of control, as opposed to transfer of risk and rewards. ASC 606 also requires enhanced disclosures regarding the nature, amount, timing, and uncertainty of revenues and cash flows from contracts with customers. Other major provisions include ensuring the time value of money is considered in the transaction price and allowing estimates of variable consideration to be recognized before contingencies are resolved in certain circumstances. ASC 606 is effective for reporting periods beginning after December 15, 2017. On January 1, 2018, we adopted the new accounting standard and all of the related amendments using the modified retrospective method. We recognized the cumulative effect of initially applying the new revenue standard as an adjustment to the opening balance of our accumulated deficit. The cumulative effect of the changes related to the adoption of the new revenue standard increased our beginning balances in accumulated deficit and deferred revenue by $203,000 within our Consolidated Balance Sheets . The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. Our Collaboration Agreement with Kite is the only contract that was impacted by the adoption of the new revenue standard. Prior to the adoption of the new revenue standard, we recognized revenue under the Collaboration Agreement based upon the estimated performance periods related to the non-refundable upfront payments we received from Kite. Under the new standard, we recognize revenue based on employee hours contributed to each performance obligation. In accordance with the new revenue standard requirements, the disclosure of the impact of adoption on our consolidated financial statements as of and for the year ended December 31, 2018 is as follows (in thousands): As Reported Adjustments Balance without Adoption of ASC 606 Consolidated Balance Sheets Stockholders’ equity Accumulated deficit $ (46,074 ) $ (203 ) $ (46,277 ) Consolidated Statements of Operations and Comprehensive Income (Loss) Collaboration revenue $ 705 $ (203 ) $ 502 Net loss (36,487 ) (203 ) (36,690 ) Statement of Cash Flows In August 2016, the FASB issued ASU No. 2016-15 which provides new guidance on the classification of certain cash receipts and payments in the statement of cash flows. The new guidance is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. We adopted this new standard effective January 1, 2018. The adoption of this standard did not impact our financial statements. Share-Based Compensation In May 2017, the FASB issued ASU No. 2017-09 to provide clarity and reduce both diversity in practice and cost and complexity when applying the guidance in Compensation - Stock Compensation (“Topic 718”) about a change to the terms and conditions of a share-based payment award. The amendments in this update provide guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The amendments in this update are effective for annual periods, including interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted and applied prospectively to modifications occurring on or after the adoption date. We adopted this this standard effective January 1, 2018. The adoption of this standard did not have an impact on our financial statements. For the year ended December 31, 2018, there were no modifications to the terms or conditions of a share-based payment award.
Net Loss Per Share	Net Loss Per Share Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. In 2016, we considered our convertible preferred stock to be participating securities, and we computed net loss per share attributable to common stockholders using the two-class method required for participating securities. All participating securities are excluded from basic weighted-average common shares outstanding. In accordance with the two-class method, earnings allocated to these participating securities, which include participation rights in undistributed earnings, are subtracted from net income to determine total undistributed earnings to be allocated to common stockholders. Net loss is not allocated to participating securities as there is no contractual obligation to share in net losses.
Fair Value Measurements	Fair Value Measurements Cash and cash equivalents, receivables, accounts payable and accrued liabilities, which are recorded at invoiced amount or cost, approximate fair value based on the short-term nature of these financial instruments. Fair value is defined as the exchange price received for an asset or paid to transfer a liability, or 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. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value, is as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 : Unobservable inputs supported by little or no market activity and significant to the fair value of the assets or liabilities.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of New Accounting Pronouncements	In accordance with the new revenue standard requirements, the disclosure of the impact of adoption on our consolidated financial statements as of and for the year ended December 31, 2018 is as follows (in thousands): As Reported Adjustments Balance without Adoption of ASC 606 Consolidated Balance Sheets Stockholders’ equity Accumulated deficit $ (46,074 ) $ (203 ) $ (46,277 ) Consolidated Statements of Operations and Comprehensive Income (Loss) Collaboration revenue $ 705 $ (203 ) $ 502 Net loss (36,487 ) (203 ) (36,690 )

Business Combination (Tables)

Business Combination (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of Fair Value of Consideration Transferred	The fair value of the consideration transferred consisted of the following (in thousands except share and per share amounts): Outstanding Nivalis common stock 3,914,058 Per share fair value of Nivalis common stock $ 9.60 Outstanding Nivalis stock options 421,992 Weighted average per share fair value of Nivalis stock options $ 1.25 Total fair value of consideration (in 000’s) $ 38,103
Schedule of Adjusted Allocation of Purchase Consideration	The final allocation of the purchase consideration is as follows (in thousands): Assets: Fair Value Cash and cash equivalents $ 31,130 Marketable securities 12,952 Other receivables 79 IPR&D 1,453 Total assets acquired 45,614 Liabilities: Accrued liabilities (401 ) Deferred tax liability (509 ) Total liabilities assumed (910 ) Bargain purchase gain (6,601 ) Total $ 38,103
Schedule of Pro Forma Financial Information	The following pro forma consolidated results of net loss for the year ended December 31, 2017 assume the business combination was completed as of January 1, 2017 (in thousands, except per share amounts): Year Ended December 31, 2017 Pro forma revenues $ 1,731 Pro forma net loss (18,327 ) Pro forma basic and diluted net loss per share $ (1.32 )

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of Anti-dilutive Securities Excluded from Diluted Net Loss Per Share Attributable to Common Stockholders Calculation	The common stock issuable upon the conversion or exercise of the following dilutive securities has been excluded from the diluted net loss per share attributable to common stockholders calculation because their effect would have been antidilutive. Diluted net loss per share, therefore, does not differ from basic net loss per share for the periods presented: December 31, 2018 2017 2016 Convertible preferred stock — — 4,311,770 Warrants to purchase common stock 24,123 24,123 12,422 Options to purchase common stock 2,509,850 1,611,996 520,739 Total 2,533,973 1,636,119 4,844,931

Cash Equivalents and Short-Te_2

Cash Equivalents and Short-Term Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Summary of Amortized Cost and Fair Value of Cash Equivalents and Short Term Investments	The amortized cost and fair value of our cash equivalents and short-term investments are as follows (in thousands): December 31, 2018 Amortized Gross Gross Fair market Money market funds $ 6,405 $ — $ — $ 6,405 U.S. treasury bills 13,966 — (2 ) 13,964 Corporate debt securities and commercial paper 31,331 — (11 ) 31,320 Total $ 51,702 $ — $ (13 ) $ 51,689 December 31, 2017 Amortized Cost Gross unrealized gains Gross unrealized losses Fair market value Money market funds $ 5,680 $ — $ — $ 5,680 U.S. treasury bills 19,909 — (21 ) 19,888 Corporate debt securities and commercial paper 53,390 — (38 ) 53,352 Total $ 78,979 $ — $ (59 ) $ 78,920

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table summarizes our financial assets and liabilities measured at fair value on a recurring basis (in thousands): Assets: December 31, 2018 Level 1 Level 2 Level 3 Total Money market funds $ 6,405 $ — $ — $ 6,405 U.S. treasury bills 13,964 — — 13,964 Corporate debt securities and commercial paper — 31,320 — 31,320 Total $ 20,369 $ 31,320 $ — $ 51,689 Assets: December 31, 2017 Level 1 Level 2 Level 3 Total Money market funds $ 5,680 $ — $ — $ 5,680 U.S. treasury bills 19,888 — — 19,888 Corporate debt securities and commercial paper — 53,352 — 53,352 Total $ 25,568 $ 53,352 $ — $ 78,920

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of property and equipment	Property and equipment, net consist of the following (in thousands): December 31, 2018 2017 Laboratory equipment $ 1,506 $ 1,161 General equipment and furniture 158 110 Computer equipment and software 103 82 Leasehold improvements 128 47 Property and equipment, at cost 1,895 1,400 Less accumulated depreciation and amortization (699 ) (311 ) Property and equipment, net $ 1,196 $ 1,089

Additional Consolidated Balan_2

Additional Consolidated Balance Sheets Information (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure Text Block Supplement [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consists of the following (in thousands): December 31, 2018 2017 Deferred financing costs $ 477 $ — Prepaid insurance 300 298 Prepaid research and development 83 791 Prepaid other 145 91 Other receivables 237 128 Prepaid expenses and other current assets $ 1,242 $ 1,308
Accounts Payable and Accrued Liabilities Disclosure	Accrued liabilities and other current liabilities consisted of the following (in thousands): December 31, 2018 2017 Research and development services $ 2,457 $ 197 Employee compensation 1,009 4 Legal and professional fees 646 112 Accrued other 165 69 Total $ 4,277 $ 382

Long-term Debt (Tables)

Long-term Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Maturities of Long-term Debt	Future principal payments as of December 31, 2018 under our loan based on contractual maturities are as follows (in thousands): Year Ending December 31, Total 2019 $ 2,000 2020 2,000 2021 — 2022 — 2023 — Total future principal payments $ 4,000

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Summary of Future Minimum Lease Payments for Non-cancelable Operating Leases	Future minimum lease payments for our non-cancelable operating leases at December 31, 2018 are as follows (in thousands): Minimum Lease Payments 2019 $ 930 2020 9 2021 9 2022 1 2023 — Total future minimum lease payments $ 949

Stockholders' Deficit (Tables)

Stockholders' Deficit (Tables)	12 Months Ended
	Dec. 31, 2018
Stockholders' Equity Note [Abstract]
Schedule of Shares of Common Stock Reserved for Future Issuance	Shares of common stock reserved for future issuance were as follows: December 31, 2018 2017 Shares to be issued upon exercise of outstanding stock options 2,509,850 1,611,996 Shares to be issued upon conversion of common stock warrants 24,123 24,123 Shares available for future stock grants 496,530 576,722 Shares to be issued under employee stock purchase plan 45,211 45,211 Shares of common stock reserved for future issuance 3,075,714 2,258,052
Schedule of Stockholders' Equity Note, Warrants or Rights	A summary of our warrant activity is presented below: Warrants Outstanding Weighted- average Exercise Price Weighted- average Remaining Contract Term (in years) Outstanding at December 31, 2017 24,123 $ 24.86 6.62 Outstanding at December 31, 2018 24,123 $ 24.86 5.62 Exercisable at December 31, 2018 17,153 $ 32.92 5.76
Schedule of Stock Option Activity	A summary of stock option activity under our plans is presented below: Options Outstanding Weighted- average Exercise Price Weighted- average Remaining Contract Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2017 1,611,996 $ 4.32 Granted 936,750 $ 8.34 Exercised (23,027 ) $ 0.39 Forfeited/Expired (15,869 ) $ 10.01 Outstanding at December 31, 2018 2,509,850 $ 5.82 8.11 $ 2,548 Vested and expected to vest after December 31, 2018 2,484,850 $ 5.81 8.10 $ 2,548 Exercisable at December 31, 2018 887,134 $ 4.26 6.66 $ 1,535
Schedule of Stock Option Assumptions	The fair values of stock options granted to employees were calculated using the following assumptions: Years Ended December 31, 2018 2017 2016 Weighted-average estimated fair value at grant $5.43 $4.69 $0.42 Risk-free interest rate (1) 2.27% - 3.07% 1.90% - 2.26% 1.14% - 2.24% Expected term of options (in years) (2) 5.50 – 7.00 5.69 – 6.32 5.22 – 7.00 Expected stock price volatility (3) 70% - 77% 72% - 83% 72% - 79% Expected dividend yield (4) —% —% —% (1) The risk-free interest rate assumption was based on zero-coupon U.S. Treasury instruments that had terms consistent with the expected term of our stock option grants. (2) We used the “simplified method” for options to determine the expected term of stock option granted to employees, since we do not have sufficient historical exercise data to provide a reasonable basis upon which to estimate expected term due to the limited time our shares have been publicly traded. Under this approach, the weighted-average expected life is presumed to be the average of the vesting term and the contractual term of the option. (3) Volatility is a measure of the amount by which a financial variable, such as share price, has fluctuated or is expected to fluctuate during a period. We analyzed the stock price volatility of companies at a similar stage of development to estimate expected volatility of our stock price. (4) We have never declared or paid any cash dividends and do not presently plan to pay cash dividends in the foreseeable future.
Schedule of Stock-based Compensation Expense	Stock-based compensation expense is classified in the Consolidated Statements of Operations and Comprehensive Income (Loss) as follows (in thousands): Years Ended December 31, 2018 2017 2016 Employee: Research and development $ 890 $ 183 $ 14 General and administrative 1,385 588 53 Non-Employee: Research and development 16 52 5 General and administrative 18 15 5 Total stock-based compensation expense $ 2,309 $ 838 $ 77

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Summary of Provision for Income Taxes	The provision for income taxes is composed of the following (in thousands): Years Ended December 31, 2018 2017 Current: U.S. - Federal $ — $ (1 ) U.S. - State (61 ) 5 Total current (61 ) 4 Deferred: U.S. - Federal (305 ) (204 ) U.S. - State — — Total deferred (305 ) (204 ) Total income tax benefit $ (366 ) $ (200 )
Summary of Effective Tax Rate of Provision for Income Taxes Differs from Federal Statutory Rate	The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows: Years Ended December 31, 2018 2017 U.S. Statutory rate 21.0 % 35.0 % Effect of: State taxes (net of federal benefit) 3.8 % (1.6 )% Permanent differences — % (0.1 )% Federal research and development credit 4.2 % 4.4 % Change in valuation allowance (27.3 )% (19.4 )% Benefit of a lower tax rate (0.1 )% 0.2 % Stock-based compensation (0.6 )% (2.6 )% Non-deductible merger costs — % (17.6 )% Bargain purchase gain — % 28.9 % Tax rate change — % (24.7 )% Effective income tax rate 1.0 % 2.5 %
Schedule of Significant Components of Deferred Tax Assets and Liabilities	The following table represents the significant components of our deferred tax assets and liabilities for the periods presented (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss $ 10,546 $ 2,475 Research and development credits 1,958 458 Intangible asset basis 54 — Deferred revenue — 58 Deferred rent 21 24 Stock based compensation 1,382 810 Other 3 12 Gross deferred tax assets 13,964 3,837 Valuation allowance (13,774 ) (3,722 ) Total deferred tax assets, net of valuation allowance 190 115 Deferred tax liabilities: Prepaid expenses (91 ) (63 ) Fixed asset basis (99 ) (110 ) Intangible asset basis — (247 ) Total deferred tax liability (190 ) (420 ) Net deferred tax assets and liabilities $ — $ (305 )
Summary of Net Operating Loss Carryforwards	We have net operating loss carryforwards as follows (in thousands): December 31, 2018 2017 Federal (before January 1, 2018) $ 11,094 $ 11,784 Federal (after January 1, 2018) $ 33,417 State $ 16,756 $ —
Summary of Net Research and Development Tax Credit Carryforwards	We have net research and development tax credit carryforwards as follows (in thousands): December 31, 2018 2017 Federal $ 2,456 $ 458
Summary of Activity Related to Unrecognized Tax benefits	The following table summarized the activity related to unrecognized tax benefits (in thousands): December 31, 2018 2017 Unrecognized benefits – beginning of year $ 114 $ 34 Gross increases (decreases) – prior year tax positions 59 (4 ) Gross increases – current year tax positions 296 84 Unrecognized benefit – end of year $ 469 $ 114

Description of Business (Detail

Description of Business (Details) $ / shares in Units, $ in Thousands	Jul. 24, 2017$ / sharesshares	Jul. 24, 2017USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)
Description Of Business [Line Items]
Convertible preferred stock, shares issued (in shares) | shares	1,335,118	1,335,118	0	0
Convertible preferred stock, purchase price per share (in dollars per share) | $ / shares	$ 12.74	$ 12.74	$ 0.001	$ 0.001
Aggregate purchase price | $		$ 17,000	$ 0	$ 37,666	$ 10,925
AIS Operating Co Inc Preexisting Stockholders, Optionholders, and Warrantholders
Description Of Business [Line Items]
Ownership percentage immediately following merger consummation		74.00%
Nivalis Therapeutics, Inc.
Description Of Business [Line Items]
Stock split conversion ratio	0.25
Ownership percentage immediately following merger consummation		26.00%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	Jul. 24, 2017	Dec. 31, 2018USD ($)segment	Jan. 01, 2019USD ($)	Jan. 01, 2018USD ($)	Dec. 31, 2017USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | segment		1
IPR&D intangible assets		$ 0			$ 1,453
Minimum percentage of income tax benefit realized upon ultimate settlement (greater than)		50.00%
Increase in accumulated deficit		$ 46,074			9,384
Increase in deferred revenue		$ 0			$ 277
Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets		5 years
Nivalis Therapeutics, Inc.
Summary Of Significant Accounting Policies [Line Items]
Stock split conversion ratio	0.25
Office And Laboratory Leases | Scenario, Forecast | Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Operating lease, right-of-use asset			$ 1,000
Operating lease, liability			$ 1,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Summary Of Significant Accounting Policies [Line Items]
Increase in accumulated deficit		$ 203		$ 203
Increase in deferred revenue				$ 203

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of New Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Stockholders’ equity
Accumulated deficit	$ (46,074)	$ (9,384)
Consolidated Statements of Operations and Comprehensive Income (Loss)
Collaboration revenue	705	1,731	$ 2,950
Net loss	(36,487)	$ (7,783)	$ (1,232)
Adjustments | Accounting Standards Update 2014-09
Stockholders’ equity
Accumulated deficit	(203)			$ (203)
Consolidated Statements of Operations and Comprehensive Income (Loss)
Collaboration revenue	(203)
Net loss	(203)
Balance without Adoption of ASC 606
Stockholders’ equity
Accumulated deficit	(46,277)
Consolidated Statements of Operations and Comprehensive Income (Loss)
Collaboration revenue	502
Net loss	$ (36,690)

Business Combination - Addition

Business Combination - Additional Information (Details) $ in Thousands	Jul. 24, 2017shares	Jul. 24, 2017USD ($)shares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)	Jul. 25, 2017shares
Business Acquisition [Line Items]
Common stock, shares outstanding (in shares) | shares			13,854,205	13,831,178		13,881,645
Aggregate purchase price		$ 17,000	$ 0	$ 37,666	$ 10,925
Bargain purchase gain			$ 0	6,601	$ 0
Acquisition-related costs				$ 1,500
Nivalis Therapeutics, Inc.
Business Acquisition [Line Items]
Stock split conversion ratio	0.25
Common stock, shares outstanding (in shares) | shares	3,914,058	3,914,058
Ownership percentage immediately following merger consummation		26.00%
Bargain purchase gain		$ 6,601
Percenatge of projected cash flows discounted to their present value using discount rate	17.00%	17.00%
Nivalis Therapeutics, Inc. | AIS Operating Co Inc Preexisting Stockholders, Optionholders, and Warrantholders
Business Acquisition [Line Items]
Exchange rate of common stock issued		0.4969
Ownership percentage immediately following merger consummation		74.00%

Business Combination - Schedule

Business Combination - Schedule of Fair Value of Consideration Transferred (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 24, 2017	Dec. 31, 2018	Dec. 31, 2017	Jul. 25, 2017
Business Acquisition [Line Items]
Outstanding Nivalis common stock (in shares)		13,854,205	13,831,178	13,881,645
Nivalis Therapeutics, Inc.
Business Acquisition [Line Items]
Outstanding Nivalis common stock (in shares)	3,914,058
Per share fair value of Nivalis common stock (in dollars per share)	$ 9.60
Outstanding Nivalis stock options (in shares)	421,992
Weighted average per share fair value of Nivalis stock options (in dollars per share)	$ 1.25
Total fair value of consideration	$ 38,103

Business Combination - Schedu_2

Business Combination - Schedule of Adjusted Allocation of Purchase Consideration (Details) - USD ($) $ in Thousands	Jul. 24, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liabilities:
Bargain purchase gain		$ 0	$ (6,601)	$ 0
Nivalis Therapeutics, Inc.
Assets:
Cash and cash equivalents	$ 31,130
Marketable securities	12,952
Other receivables	79
IPR&D	1,453		$ 1,500
Total assets acquired	45,614
Liabilities:
Accrued liabilities	(401)
Deferred tax liability	(509)
Total liabilities assumed	(910)
Bargain purchase gain	(6,601)
Total	$ 38,103

Business Combination - Schedu_3

Business Combination - Schedule of Pro Forma Financial Information (Details) - Nivalis Therapeutics, Inc. $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)$ / shares
Business Acquisition [Line Items]
Pro forma revenues	$ 1,731
Pro forma net loss	$ (18,327)
Pro forma basic and diluted net loss per share (in dollars per share) | $ / shares	$ (1.32)

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Convertible preferred stock converted to common stock (in shares)	9,301,433
Nivalis Therapeutics, Inc.
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Common stock acquired in business combination (in shares)	3,914,058

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Anti-dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,533,973	1,636,119	4,844,931
Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0	4,311,770
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	24,123	24,123	12,422
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,509,850	1,611,996	520,739

Cash Equivalents and Short-Te_3

Cash Equivalents and Short-Term Investments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 51,702,000	$ 78,979,000
Gross unrealized gains	0	0
Gross unrealized losses	(13,000)	(59,000)
Fair market value	51,689,000	78,920,000
Realized gains and losses on securities	0	0
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,405,000	5,680,000
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair market value	6,405,000	5,680,000
U.S. treasury bills
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	13,966,000	19,909,000
Gross unrealized gains	0	0
Gross unrealized losses	(2,000)	(21,000)
Fair market value	13,964,000	19,888,000
Corporate debt securities and commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31,331,000	53,390,000
Gross unrealized gains	0	0
Gross unrealized losses	(11,000)	(38,000)
Fair market value	$ 31,320,000	$ 53,352,000

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Cash	$ 614	$ 2,300

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	$ 51,689	$ 78,920
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	6,405	5,680
U.S. treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	13,964	19,888
Corporate debt securities and commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	31,320	53,352
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	20,369	25,568
Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	6,405	5,680
Level 1 | U.S. treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	13,964	19,888
Level 1 | Corporate debt securities and commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	31,320	53,352
Level 2 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Level 2 | U.S. treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Level 2 | Corporate debt securities and commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	31,320	53,352
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Level 3 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Level 3 | U.S. treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	0	0
Level 3 | Corporate debt securities and commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value assets disclosure	$ 0	$ 0

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 1,895	$ 1,400
Less accumulated depreciation and amortization	(699)	(311)
Property and equipment, net	1,196	1,089
Depreciation expenses	388	241	$ 69
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	1,506	1,161
General equipment and furniture
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	158	110
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	103	82
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 128	$ 47

Loss on Sale of Intangible As_2

Loss on Sale of Intangible Assets (Details) - USD ($) $ in Thousands	1 Months Ended			12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Feb. 28, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Revenues				$ 705	$ 1,731	$ 2,950
Proceeds from sale of intangible asset				250	0	0
Loss on sale of intangible asset				1,203	$ 0	$ 0
Laurel Venture Capital Ltd. | GSNOR
Finite-Lived Intangible Assets [Line Items]
Proceeds from sale of intangible asset		$ 250
Potential milestone payments eligible to be received		20,000
Loss on sale of intangible asset				$ 1,200
Laurel Venture Capital Ltd. | GSNOR | Term Sheet
Finite-Lived Intangible Assets [Line Items]
Revenues			$ 75
Scenario, Forecast | Laurel Venture Capital Ltd. | GSNOR
Finite-Lived Intangible Assets [Line Items]
Potential milestone payments eligible to be received	$ 425
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Laurel Venture Capital Ltd. | GSNOR
Finite-Lived Intangible Assets [Line Items]
Intangible assets, amount derecognized upon sale		$ 1,500

Additional Consolidated Balan_3

Additional Consolidated Balance Sheets Information - Prepaid Expense and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Disclosure Text Block Supplement [Abstract]
Deferred financing costs	$ 477	$ 0
Prepaid insurance	300	298
Prepaid research and development	83	791
Prepaid other	145	91
Other receivables	237	128
Prepaid expenses and other current assets	$ 1,242	$ 1,308

Additional Consolidated Balan_4

Additional Consolidated Balance Sheets Information - Accrued Liabilities and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Disclosure Text Block Supplement [Abstract]
Research and development services	$ 2,457	$ 197
Employee compensation	1,009	4
Legal and professional fees	646	112
Accrued other	165	69
Total	$ 4,277	$ 382

Long-term Debt - Narrative (De

Long-term Debt - Narrative (Details)	Jun. 30, 2017USD ($)payment$ / sharesshares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jul. 24, 2017shares
Debt Instrument [Line Items]
Term loan drew down		$ 0	$ 5,000,000	$ 0
Number of equal monthly payments | payment	30
Amortization of debt discount		169,000	$ 87,000
Unamortized debt discount		$ 172,000
Common Stock
Debt Instrument [Line Items]
Warrants exercisable for shares of common stock (in shares) | shares					7,069
Series A-1 Preferred Stock Warrants
Debt Instrument [Line Items]
Warrants issued, exercise price (in dollars per share) | $ / shares	$ 12.38
Fair value of warrant liability	$ 53,000
Warrants exercisable for shares of common stock (in shares) | shares	7,069
Term Loan
Debt Instrument [Line Items]
Term loan drew down	$ 5,000,000
Long-term debt final payment fee percentage	7.50%
Long-term debt final payment fee	$ 375,000
Term Loan | Prime Rate
Debt Instrument [Line Items]
Debt instrument variable interest rate	1.75%

Long-term Debt - Schedule of Ma

Long-term Debt - Schedule of Maturities of Long-term Debt (Details) $ in Thousands	Dec. 31, 2018USD ($)
Debt Disclosure [Abstract]
2019	$ 2,000
2020	2,000
2021	0
2022	0
2023	0
Total future principal payments	$ 4,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Mar. 18, 2019USD ($)ft²term	Jan. 31, 2018USD ($)ft²term	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)ft²term	May 31, 2017USD ($)
Loss Contingencies [Line Items]
Office and laboratory space | ft²					11,158
Operating lease, annual base rent		$ 295			$ 566
Operating lease, annual base rent increasing percentage		3.00%			3.00%
Number of option to extend term lease | term		2			2
Operating lease renewal term		12 months			12 months
Rent expense			$ 811	$ 529	$ 267
Additional office and laboratory space | ft²		6,184
Line of Credit
Loss Contingencies [Line Items]
Security deposit						$ 132
Subsequent Event
Loss Contingencies [Line Items]
Operating lease, annual base rent	$ 1,700
Operating lease, annual base rent increasing percentage	3.00%
Number of option to extend term lease | term	1
Operating lease renewal term	5 years
Additional office and laboratory space | ft²	27,164
Term of contract	10 years 9 months 18 days
Maximum tenant improvement allowance	$ 5,400
Additional maximum tenant improvement allowance	$ 1,800
Percentage of tenant improvement allowance	8.00%
Subsequent Event | Line of Credit
Loss Contingencies [Line Items]
Security deposit	$ 254

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Future Minimum Lease Payments for Non-cancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019	$ 930
2020	9
2021	9
2022	1
2023	0
Total future minimum lease payments	$ 949

Collaboration and License Agr_2

Collaboration and License Agreement (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Oct. 31, 2017USD ($)program	Oct. 31, 2015USD ($)program	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues			$ 705	$ 1,731	$ 2,950
Kite | Collaboration and Licensing Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of programs | program		2
Deferred revenue		$ 5,500
Eligible to receive additional research support payment	$ 450
Number of tranches | program	2
Revenues			630	$ 1,700	$ 2,900
Accounting Standards Update 2014-09 | Adjustments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues			(203)
Revenue recognized			(203)
Maximum | Kite | Collaboration and Licensing Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future milestones receivable (up to)			$ 530,000

Stockholders' Deficit - Additio

Stockholders' Deficit - Additional Information (Details) $ / shares in Units, $ in Thousands

Jan. 01, 2019shares

Jun. 11, 2018USD ($)

Jan. 31, 2019USD ($)$ / sharesshares

Aug. 31, 2018shares

Jun. 30, 2018USD ($)shares

Dec. 31, 2017USD ($)$ / sharesshares

Jul. 31, 2016USD ($)

May 31, 2016employeeshares

Dec. 31, 2018USD ($)shares

Dec. 31, 2017USD ($)shares

Dec. 31, 2016USD ($)

Jul. 31, 2017shares

Jul. 25, 2017shares

Jul. 24, 2017shares

Class of Stock [Line Items]

Convertible preferred stock converted to common stock (in shares)

9,301,433

9,301,433

Common stock, shares outstanding (in shares)

13,831,178

13,854,205

13,831,178

13,881,645

Repurchase of unvested common stock (in shares)

50,467

50,467

50,467

Original purchase price (in dollars per share) | $ / shares

$ 0.002

Maximum amount of common stock eligible to be sold | $

$ 14,500

Deferred financing costs | $

$ 0

$ 477

$ 0

Shares available for future issuance (in shares)

2,258,052

3,075,714

2,258,052

Vesting period (in years)

4 years

4 years

Term (in years)

10 years

10 years

Extended vesting period of number of unvested share options (in shares)

567,500

Number of employees | employee

5

Additional compensation expense | $

$ 4

Options to purchase common stock

Class of Stock [Line Items]

Unrecognized compensation cost related to nonvested stock options | $

$ 6,500

Weighted-average period over which unrecognized compensation expense related to nonvested stock options is expected to be recognized

2 years 10 months 24 days

Aggregate intrinsic value of stock options exercised | $

$ 214

$ 18

22

Fair value of shares vested | $

$ 1,800

$ 139

$ 70

2018 Plan

Class of Stock [Line Items]

Percentage of outstanding stock maximum

5.00%

2018 Plan | Common Stock Initial Reserves

Class of Stock [Line Items]

Number of shares authorized (in shares)

901,530

2018 Plan | Legacy Plan Cancellations

Class of Stock [Line Items]

Number of shares authorized (in shares)

1,972,784

Inducement Grant

Class of Stock [Line Items]

Number of shares authorized (in shares)

150,000

Incentive Stock Option

Class of Stock [Line Items]

Term (in years)

10 years

Stock Plan 2018, Stock Plan 2015 And Equity Incentive Plan 2015

Class of Stock [Line Items]

Number of shares authorized (in shares)

3,061,084

Stock Plan 2018

Class of Stock [Line Items]

Shares available for future issuance (in shares)

496,530

Common Stock

Class of Stock [Line Items]

Convertible preferred stock converted to common stock (in shares)

9,301,433

Warrants exercisable (in shares)

7,069

Employee Stock

Class of Stock [Line Items]

Shares available for future issuance (in shares)

45,211

Cowen and Company, LLC

Class of Stock [Line Items]

Maximum amount of common stock eligible to be sold | $

$ 30,000

Piper Jaffray & Co.

Class of Stock [Line Items]

Maximum amount of common stock eligible to be sold | $

$ 50,000

Percentage of compensation for services

3.00%

Maximum | 2018 Plan

Class of Stock [Line Items]

Additional number of shares authorized (in shares)

1,500,000

Subsequent Event

Class of Stock [Line Items]

Proceeds from issuance of private placement | $

$ 25,300

Shares issued (in shares)

4,706,700

Per unit, common stock to warrant ratio (in shares)

0.39

Purchase price per unit (in dollars per unit) | $ / shares

$ 5.37

Warrants exercisable (in shares)

1,835,610

Warrants issued, exercise price (in dollars per share) | $ / shares

$ 12.74

Term of warrants

5 years

Subsequent Event | 2018 Plan

Class of Stock [Line Items]

Additional number of shares authorized (in shares)

692,710

Subsequent Event | Common Stock

Class of Stock [Line Items]

Proceeds from issuance of private placement | $

$ 5,000

Shares issued (in shares)

935,753

Stockholders' Deficit - Schedul

Stockholders' Deficit - Schedule of Shares of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	3,075,714	2,258,052
Shares to be issued upon exercise of outstanding stock options
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	2,509,850	1,611,996
Shares to be issued upon conversion of common stock warrants
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	24,123	24,123
Shares available for future stock grants
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	496,530	576,722
Shares to be issued under employee stock purchase plan
Class of Stock [Line Items]
Shares of common stock reserved for future issuance (in shares)	45,211	45,211

Stockholders' Deficit - Sched_2

Stockholders' Deficit - Schedule of Warrants (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Warrants Outstanding (in shares)	24,123	24,123
Warrants exercisable (in shares)	17,153
Weighted average, exercise price (in dollars per share)	$ 24.86	$ 24.86
Weighted average, exercisable (in dollars per share)	$ 32.92
Weighted- average Remaining Contract Term	5 years 7 months 13 days	6 years 7 months 13 days
Weighted- average Remaining Contract Term, Exercisable	5 years 9 months 4 days

Stockholders' Deflicit - Summar

Stockholders' Deflicit - Summary of Option Activity (Details) - Options to purchase common stock - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Options Outstanding
Outstanding at beginning of period (in shares)	1,611,996
Granted (in shares)	936,750
Exercised (in shares)	(23,027)
Forfeited/Expired (in shares)	(15,869)
Outstanding at ending of period (in shares)	2,509,850	1,611,996
Vested and expected to vest (in shares)	2,484,850
Exercisable (in shares)	887,134
Weighted- average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 4.32
Granted (in dollars per share)	8.34
Exercised (in dollars per share)	0.39
Forfeited/Expired (in dollars per share)	10.01
Outstanding at ending of period (in dollars per share)	5.82	$ 4.32
Vested and expected to vest (in dollars per share)	5.81
Exercisable (in dollars per share)	$ 4.26
Weighted- average Remaining Contract Term (in years)
Outstanding (in years)	8 years 1 month 11 days
Vested and expected to vest (in years)	8 years 1 month 6 days
Exercisable (in years)	6 years 7 months 27 days
Aggregate Intrinsic Value
Beginning balance
Ending balance	2,548
Vested and expected to vest	2,548
Exercisable	$ 1,535

Stockholders' Deficit - Sched_3

Stockholders' Deficit - Schedule of Stock Option Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average estimated fair value at grant (in dollars per share)	$ 5.43	$ 4.69	$ 0.42
Risk-free interest rate, minimum	2.27%	1.90%	1.14%
Risk-free interest rate, maximum	3.07%	2.26%	2.24%
Expected stock price volatility, minimum	70.00%	72.00%	72.00%
Expected stock price volatility, maximum	77.00%	83.00%	79.00%
Expected dividend yield	0.00%	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of options (in years)	5 years 6 months	5 years 8 months 9 days	5 years 2 months 19 days
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of options (in years)	7 years	6 years 3 months 26 days	7 years

Stockholders' Deficit - Sched_4

Stockholders' Deficit - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,309	$ 838	$ 77
Employee | Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	890	183	14
Employee | General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,385	588	53
Non-Employee | Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	16	52	5
Non-Employee | General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 18	$ 15	$ 5

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 24, 2017
Income Taxes [Line Items]
Tax benefit	$ 366,000	$ 200,000	$ (66,000)
Effective tax rate	1.00%	2.50%
Increase in valuation allowance	$ 10,000,000	$ 2,900,000
Unrecognized tax benefits	469,000	114,000	$ 34,000
Accrued interest or penalties related to unrecognized tax benefits	0	0
Nivalis Therapeutics, Inc.
Income Taxes [Line Items]
IPR&D acquired in business combination		1,500,000		$ 1,453,000
Deferred tax liability, IPR&D		305,000
IPR&D acquired in business combination, tax basis		$ 0
Tax credit and net operating loss carryforwards	$ 0

Income Taxes - Summary of Provi

Income Taxes - Summary of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
U.S. - Federal	$ 0	$ (1)
U.S. - State	(61)	5
Total current	(61)	4
Deferred:
U.S. - Federal	(305)	(204)
U.S. - State	0	0
Total deferred	(305)	(204)
Total income tax benefit	$ (366)	$ (200)	$ 66

Income Taxes - Summary of Effec

Income Taxes - Summary of Effective Tax Rate of Provision for Income Taxes Differs from Federal Statutory Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. Statutory rate	21.00%	35.00%
Effect of:
State taxes (net of federal benefit)	3.80%	(1.60%)
Permanent differences	(0.00%)	(0.10%)
Federal research and development credit	4.20%	4.40%
Change in valuation allowance	(27.30%)	(19.40%)
Benefit of a lower tax rate	(0.10%)	0.20%
Stock-based compensation	(0.60%)	(2.60%)
Non-deductible merger costs	0.00%	(17.60%)
Bargain purchase gain	0.00%	28.90%
Tax rate change	0.00%	(24.70%)
Effective income tax rate	1.00%	2.50%

Income Taxes - Schedule of Sign

Income Taxes - Schedule of Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss	$ 10,546	$ 2,475
Research and development credits	1,958	458
Intangible asset basis	54	0
Deferred revenue	0	58
Deferred rent	21	24
Stock based compensation	1,382	810
Other	3	12
Gross deferred tax assets	13,964	3,837
Valuation allowance	(13,774)	(3,722)
Total deferred tax assets, net of valuation allowance	190	115
Deferred tax liabilities:
Prepaid expenses	(91)	(63)
Fixed asset basis	(99)	(110)
Intangible asset basis	0	(247)
Total deferred tax liability	(190)	(420)
Net deferred tax assets and liabilities	$ 0	$ (305)

Income Taxes - Summary of Net O

Income Taxes - Summary of Net Operating Loss Carryforwards (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
State
Income Taxes [Line Items]
Net operating loss carryforwards	$ 16,756	$ 0
Before January 1 2018 | Federal
Income Taxes [Line Items]
Net operating loss carryforwards	11,094	$ 11,784
After January 1 2018 | Federal
Income Taxes [Line Items]
Net operating loss carryforwards	$ 33,417

Income Taxes - Summary Tax Cred

Income Taxes - Summary Tax Credit Carryforwards (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Research and development credits	$ 1,958	$ 458
Federal
Income Taxes [Line Items]
Research and development credits	$ 2,456	$ 458

Income Taxes - Summary of Activ

Income Taxes - Summary of Activity Related to Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized benefits – beginning of year	$ 114	$ 34
Gross increases (decreases) – prior year tax positions	59
Gross increases (decreases) – prior year tax positions		(4)
Gross increases – current year tax positions	296	84
Unrecognized benefit – end of year	$ 469	$ 114

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Alpine BioVentures GP, LLC
Related Party Transaction [Line Items]
Expenses related to shared services agreement		$ 0	$ 0	$ 17
Accrued expenses related to shared services agreement				$ 5
Subsequent Event
Related Party Transaction [Line Items]
Shares sold (in shares)	4,706,700
Proceeds from exercise of stock options and common stock warrants	$ 25,300
Common Stock | Subsequent Event
Related Party Transaction [Line Items]
Shares sold (in shares)	935,753
Warrants issued to purchase shares of common stock (in shares)	364,943
Proceeds from exercise of stock options and common stock warrants	$ 5,000
Ownership percentage by noncontrolling owners	5.00%

Uncategorized Items - alpn-2018

Label	Element	Value
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (203,000)