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Document and Entity Information - shares
6 Months Ended
Jun. 30, 2020
Aug. 06, 2020
Document Document and Entity Information [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Document Period End Date Jun. 30, 2020  
Entity File Number 001-34475  
Entity Registrant Name OMEROS CORPORATION  
Entity Incorporation, State or Country Code WA  
Entity Tax Identification Number 91-1663741  
Entity Address, Address Line One 201 Elliott Avenue West  
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 676-5000  
Title of 12(b) Security Common Stock  
Trading Symbol OMER  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   54,518,358
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q2  
Entity Central Index Key 0001285819  
Amendment Flag false