v3.24.1.u1

Cover - USD ($) $ in Millions	12 Months Ended
Cover - USD ($) $ in Millions	Dec. 31, 2023	Apr. 09, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K/A
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-37449
Entity Registrant Name	ALPINE IMMUNE SCIENCES, INC.
Entity Incorporation, Date of Incorporation	DE
Entity Tax Identification Number	20-8969493
Entity Address, Address Line One	188 East Blaine Street
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	Seattle,
Entity Address, State or Province	WA
Entity Address, Postal Zip Code	98102
City Area Code	206
Local Phone Number	788-4545
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	ALPN
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 349.1
Entity Common Stock, Shares Outstanding		65,560,484
Documents Incorporated by Reference	None.
Entity Central Index Key	0001626199
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
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ALPINE IMMUNE SCIENCES, INC. 10-K/A