v3.19.2
Cover - shares
6 Months Ended
Jun. 30, 2019
Aug. 08, 2019
Cover page.    
Document Type 10-Q  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Document Quarterly Report true  
Document Transition Report false  
Entity File Number 001-37449  
Entity Registrant Name ALPINE IMMUNE SCIENCES, INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 20-8969493  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding (in shares)   18,587,644
Title of 12(b) Security Common Stock, par value $0.001 per share  
Trading Symbol ALPN  
Security Exchange Name NASDAQ  
Entity Central Index Key 0001626199  
Current Fiscal Year End Date --12-31  
Entity Ex Transition Period true  
Entity Address, Address Line One 201 Elliott Avenue West, Suite 230  
Entity Address, City or Town Seattle  
Entity Address, State or Province WA  
Entity Address, Postal Zip Code 98119  
City Area Code 206  
Local Phone Number 788-4545