Certain Balance Sheet Accounts - Contract Royalty Asset (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Certain Balance Sheet Accounts
Short-term contract royalty asset	$ 28,940	$ 28,797
Long-term contract royalty asset	119,681	123,425
Total OMIDRIA contract royalty asset	$ 148,621	$ 152,222

Amount of contract royalty asset due to the entity within one year of the balance sheet date (or one operating cycle, if longer).

No definition available.

Name:	omer_ContractRoyaltyAssetCurrent
Namespace Prefix:	omer_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant