Note 10 - Commitments and Contingencies (Details Textual) $ in Millions	Mar. 31, 2026 USD ($)
Long-Term Purchase Commitment, Termination Fee	$ 25.8

Represents the amount of termination fee on a long-term purchase commitment.

No definition available.

Name:	omer_LongtermPurchaseCommitmentTerminationFee
Namespace Prefix:	omer_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant