| Document and Entity Information | May 20, 2021 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Oct. 1, 2021 |
| Entity Registrant Name | OMEROS CORPORATION |
| Entity Central Index Key | 0001285819 |
| Entity Incorporation, State or Country Code | WA |
| Entity File Number | 001-34475 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, $0.01 par value per share |
| Trading Symbol | OMER |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
