v3.10.0.1
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2018
Feb. 25, 2019
Jun. 30, 2018
Document Documentand Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Trading Symbol OMER    
Entity Registrant Name OMEROS CORP    
Entity Central Index Key 0001285819    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Large Accelerated Filer    
Entity Common Stock, Shares Outstanding   49,011,735  
Entity Public Float     $ 827,171,756