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Note 6 - Debt (Details Textual) |  |  |  |  |  | 1 Months Ended | 2 Months Ended | 3 Months Ended | 6 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 30, 2025 USD ($) $ / shares shares | May 14, 2025 USD ($) $ / shares shares | May 12, 2025 USD ($) | Jun. 03, 2024 USD ($) | May 14, 2024 USD ($) | Aug. 14, 2025 shares | Aug. 11, 2025 shares | Jun. 30, 2025 USD ($) $ / shares shares | Jun. 30, 2025 USD ($) $ / shares shares | Jun. 30, 2025 USD ($) $ / shares | Jun. 30, 2024 USD ($) | Jun. 30, 2025 USD ($) $ / shares | Jun. 30, 2024 USD ($) | Jun. 03, 2026 | Nov. 01, 2025 USD ($) | Jun. 03, 2025 | May 15, 2025 USD ($) | May 13, 2025 USD ($) | Dec. 31, 2024 USD ($)
Gain (Loss) on Extinguishment of Debt |  |  |  |  |  |  |  |  |  |  | $ (2,968,000) | $ 0 | $ (2,968,000) | $ 0 |  |  |  |  |  |
Unrealized Gain (Loss) on Derivatives |  |  |  |  |  |  |  |  |  |  | 8,207,000 | $ 0 | 8,142,000 | 0 |  |  |  |  |  |
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount, Current |  | $ 7,627,000 |  |  |  |  |  |  | $ 7,627,000 | $ 7,627,000 | 7,627,000 |  | 7,627,000 |  |  |  |  |  |  | $ 0
Long-Term Debt, Gross |  | 167,804,000 |  |  |  |  |  |  | 167,804,000 | 167,804,000 | 167,804,000 |  | 167,804,000 |  |  |  |  |  |  |
Financial Instrument, Mandatorily Redeemable, Liability Classified, Settlement, Amount |  |  |  |  |  |  |  |  | 3,300,000 |  |  |  |  |  |  |  |  |  |  |
Payments of Debt Restructuring Costs |  |  |  |  |  |  |  |  |  |  |  |  | $ (0) | $ 21,179,000 |  |  |  |  |  |
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] |  |  |  |  | Secured Overnight Financing Rate (SOFR) [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Convertible Senior Notes 2026 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date |  |  | Jun. 15, 2029 |  |  |  |  |  |  |  |  |  | Feb. 15, 2026 |  |  |  |  |  |  |
Convertible Debt, Fair Value Disclosures | [1] | 16,048,000 |  |  |  |  |  |  | 16,048,000 | 16,048,000 | 16,048,000 |  | $ 16,048,000 |  |  |  |  |  |  | 93,752,000
Debt Issuance Costs, Net |  | $ 100,000 |  |  |  |  |  |  | $ 100,000 | $ 100,000 | $ 100,000 |  | $ 100,000 |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 5.25% | 5.25% |  |  |  |  |  | 5.25% | 5.25% | 5.25% |  | 5.25% |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 5.89% |  |  |  |  |  |  | 5.89% | 5.89% | 5.89% |  | 5.89% |  |  |  |  |  |  |
Debt Instrument, Convertible, Conversion Ratio |  |  |  |  |  |  |  |  |  |  |  |  | 54.0906 |  |  |  |  |  |  |
Debt Instrument, Convertible Debt, Denominator Amount |  | $ 1,000 |  |  |  |  |  |  | $ 1,000 | $ 1,000 | $ 1,000 |  | $ 1,000 |  |  |  |  |  |  |
Debt Instrument, Convertible, Conversion Price | $ / shares |  | $ 18.4875 |  |  |  |  |  |  | $ 18.4875 | $ 18.4875 | $ 18.4875 |  | $ 18.4875 |  |  |  |  |  |  |
Debt Instrument, Convertible, Number of Equity Instruments |  |  |  |  |  |  |  |  |  |  |  |  | 1,300,000 |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Trading Days |  |  | 20 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt, Gross |  | $ 17,017,000 | $ 17,100,000 |  |  |  |  |  | $ 17,017,000 | $ 17,017,000 | $ 17,017,000 |  | $ 17,017,000 |  |  |  |  |  | $ 97,900,000 | 97,178,000
Principal amount |  | $ 17,077,000 |  |  | $ 14,900,000 |  |  |  | $ 17,077,000 | $ 17,077,000 | $ 17,077,000 |  | $ 17,077,000 |  |  |  |  |  |  | 97,862,000
Debt Instrument, Covenant, Minimum Principal Amount Required to Trigger Prepayment |  |  | 38,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Mandatory Prepayment |  |  | $ 20,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Convertible Senior Notes 2026 [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Conversion Price | $ / shares |  |  | $ 2.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Convertible Senior Notes 2026 [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Conversion Price | $ / shares |  | $ 18.49 |  |  |  |  |  |  | $ 18.49 | $ 18.49 | $ 18.49 |  | $ 18.49 |  |  |  |  |  |  |
Convertible Senior Notes 2026 [Member] | Debt Conversion After September 30, 2020 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible Debt, Denominator Amount |  | $ 1,000 |  |  |  |  |  |  | $ 1,000 | $ 1,000 | $ 1,000 |  | $ 1,000 |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger |  |  |  |  |  |  |  |  |  |  |  |  | 130.00% |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Consecutive Trading Days |  |  |  |  |  |  |  |  |  |  |  |  | 5 |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Sale Price Of Common Stock Conversion Rate Product Percentage Maximum |  | 98.00% |  |  |  |  |  |  | 98.00% | 98.00% | 98.00% |  | 98.00% |  |  |  |  |  |  |
Convertible Senior Notes 2026 [Member] | Debt Conversion On Or After August 15, 2023 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Trading Days Before Maturity |  |  |  |  |  |  |  |  |  |  |  |  | 50 days |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger |  |  |  |  |  |  |  |  |  |  |  |  | 130.00% |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Trading Days |  |  |  |  |  |  |  |  |  |  |  |  | 30 |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Consecutive Trading Days |  |  |  |  |  |  |  |  |  |  |  |  | 20 |  |  |  |  |  |  |
The 2029 Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date |  |  | Jun. 15, 2029 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Convertible Debt, Fair Value Disclosures | [2] | $ 59,263,000 |  |  |  |  |  |  | $ 59,263,000 | $ 59,263,000 | $ 59,263,000 |  | $ 59,263,000 |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 9.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 1.82% |  |  |  |  |  |  | 1.82% | 1.82% | 1.82% |  | 1.82% |  |  |  |  |  |  |
Debt Instrument, Convertible, Conversion Ratio |  |  | 161.81 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible Debt, Denominator Amount |  |  | $ 1,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Conversion Price | $ / shares |  |  | $ 6.18 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Number of Equity Instruments |  |  | 11,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Period After Conversion Date for Interest Payment |  |  | 18 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Embedded Derivative, Fair Value of Embedded Derivative, Net |  | $ (15,020,000) |  |  |  |  |  |  | $ (15,020,000) | $ (15,020,000) | $ (15,020,000) |  | $ (15,020,000) |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount |  |  | $ 20,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Trading Days Before Maturity |  |  | 50 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger |  |  | 130.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Trading Days |  |  | 20 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Consecutive Trading Days |  |  | 30 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Default, Declared Payable in Full, Percentage of Holders of Debt |  |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Default, Special Interest Period |  |  | 180 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt, Gross |  | 63,474,000 |  |  |  |  |  |  | 63,474,000 | 63,474,000 | 63,474,000 |  | 63,474,000 |  |  |  |  |  |  |
Principal amount |  | 70,785,000 |  |  |  |  |  |  | 70,785,000 | 70,785,000 | 70,785,000 |  | 70,785,000 |  |  |  |  |  |  |
The 2029 Notes [Member] | Conversion Option Derivative [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Embedded Derivative, Fair Value of Embedded Derivative, Net |  | $ (15,000,000) | $ (23,000,000) |  |  |  |  |  | (15,000,000) | $ (15,000,000) | $ (15,000,000) |  | $ (15,000,000) |  |  |  |  | $ (23,000,000) |  |
Unrealized Gain (Loss) on Derivatives |  |  |  |  |  |  |  |  | $ 8,000,000 |  |  |  |  |  |  |  |  |  |  |
The Credit and Guaranty Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Maturity Date |  |  |  |  | Jun. 03, 2028 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 13.17% |  |  |  |  |  |  | 13.17% | 13.17% | 13.17% |  | 13.17% |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage |  | 3.44% |  |  |  |  |  |  | 3.44% | 3.44% | 3.44% |  | 3.44% |  |  |  |  |  |  |
Debt Instrument, Default, Declared Payable in Full, Percentage of Holders of Debt |  |  |  |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Floor on Variable Rate |  |  |  |  | 3.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Basis Spread on Variable Rate |  |  |  |  | 8.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Percentage of Interest Payable in Cash |  |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Paid In Kind, Basis Spread on Variable Rate |  |  |  |  | 10.25% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Prepayment, Percentage of Milestone Payments Received |  |  |  |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Prepayment, Percentage of Cash Proceeds From Sale or License of Assets |  |  |  |  | 60.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Prepayment, Percentage of Cash Proceeds From Indebtedness |  |  |  |  | 100.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Prepayment, Percentage of Net Cash Proceeds From Insurance Recoveries |  |  |  |  | 100.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Prepayments, Annual Prepayment Percentage |  |  |  |  | 5.00% |  |  |  |  |  |  |  |  |  |  |  | 5.00% |  |  |
Debt Instrument, Covenant, Required Unrestricted Cash |  | $ 25,000,000 |  |  | $ 25,000,000 |  |  |  | $ 25,000,000 | $ 25,000,000 | $ 25,000,000 |  | $ 25,000,000 |  |  |  |  |  |  |
Debt Instrument, Covenant, Open Market Transactions, Maximum Amount of Initial Cash |  |  |  |  | 25,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Open Market Transactions, Conditional Additional Amount |  |  |  |  | 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Open Market Transactions, Unlimited Threshold |  |  |  |  | $ 38,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Open Market Transactions, Maximum Additional Amount, Percentage of Proceeds From Equity Offering |  |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-Term Debt, Fair Value |  | 69,900,000 |  |  |  |  |  |  | 69,900,000 | 69,900,000 | 69,900,000 |  | $ 69,900,000 |  |  |  |  |  |  | $ 69,500,000
The Credit and Guaranty Agreement [Member] | Forecast [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Covenant, Minimum Principal Amount Required to Trigger Prepayment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 38,500,000 |  |  |  |
Debt Instrument, Covenant, Mandatory Prepayment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,000,000 |  |  |  |
Debt Instrument, Covenant, Prepayment Premium |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000,000 |  |  |  |
Debt Instrument, Prepayments, Annual Prepayment Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.00% |  |  |  |  |
The Credit and Guaranty Agreement [Member] | Initial Term Loan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  | $ 67,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
The 2026 Capped Call [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Number of Equity Instruments |  |  |  |  |  |  |  |  |  |  |  |  | 12,200,000 |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Trading Days |  |  |  |  |  |  |  |  |  |  |  |  | 50 |  |  |  |  |  |  |
Debt Instrument, Convertible, Fair Value Amount of Equity Component |  | $ 23,200,000 |  |  |  |  |  |  | $ 23,200,000 | $ 23,200,000 | $ 23,200,000 |  | $ 23,200,000 |  |  |  |  |  |  |
The 2026 Capped Call [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Conversion Price | $ / shares |  | $ 18.49 |  |  |  |  |  |  | $ 18.49 | $ 18.49 | $ 18.49 |  | $ 18.49 |  |  |  |  |  |  |
The 2026 Capped Call [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Conversion Price | $ / shares |  | $ 26.1 |  |  |  |  |  |  | $ 26.1 | $ 26.1 | $ 26.1 |  | $ 26.1 |  |  |  |  |  |  |
Conversion of the 2026 Notes Into 2029 Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Conversion, Original Debt, Net Amount |  |  | 70,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Convertible Debt, Fair Value Disclosures |  |  | 73,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Conversion, Original Debt, Amount |  |  | 70,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Issuance Costs, Net |  |  | 400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Extinguishment of Debt |  |  | 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion of the 2026 Notes Into Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Conversion, Original Debt, Amount |  |  | $ 10,000,000 | $ 10,000,000 |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Trading Days |  |  | 20 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Conversion, Converted Instrument, Shares Issued | shares |  | 539,320 | 10,000,000 |  |  |  |  |  | 539,320 | 539,320 |  |  |  |  |  |  |  |  |  |
Conversion of the 2026 Notes Into Common Stock [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Conversion, Converted Instrument, Shares Issued | shares |  |  |  |  |  |  | 1,996,555 | 1,996,555 |  |  |  |  |  |  |  |  |  |  |  |
Conversion of 2026 Notes Into Common Stock and 2029 Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Conversion, Original Debt, Amount |  |  | $ 80,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion of 2026 Notes into New Term Loans [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Conversion, Original Debt, Amount |  |  |  |  | 118,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments of Debt Restructuring Costs |  |  |  |  | 21,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of Debt |  |  |  |  | $ 88,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed |  |  |  |  | 75.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Increase (Decrease), Net |  |  |  |  | $ (51,000,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Premium |  |  |  |  | $ 29,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
[1] | The fair value is classified as Level 2 liability due to the limited trading activity for the 2026 Notes. This balance reflects the fair value of the 2026 Notes based on quoted prices in an over-the counter market using the most recent trading information at the end of the reporting period. The value of the conversion feature of the 2026 Notes is not deemed to be significant as the current market price of our common stock is below the initial conversion price of $18.49 per share of common stock.
[2] | The fair value is classified as a Level 2 liability due to the limited trading activity for the 2029 Notes. This balance reflects the fair value of the 2029 Notes based on quoted prices in an over-the counter market using the most recent trading information at the end of the reporting period.

X
- Definition The net amount of the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References No definition available. + Details
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Namespace Prefix: | omer_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the denominator amount used in the calculation of convertible debt. + References No definition available. + Details
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Namespace Prefix: | omer_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The fair value amount of the equity component of convertible debt which may be settled in cash upon conversion. + References No definition available. + Details
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Namespace Prefix: | omer_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Period after conversion for interest payments on convertible debt instruments. + References No definition available. + Details
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Namespace Prefix: | omer_
Data Type: | xbrli:durationItemType
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X
- Definition Represents the amount of principal on f a debt instrument that can be converted to another debt instrument. + References No definition available. + Details
Name: | omer_DebtInstrumentConvertiblePrincipalAmount
Namespace Prefix: | omer_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Represents the maximum product of the closing sale price of shares of the entity's common stock and the applicable conversion rate for such trading day. + References No definition available. + Details
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Namespace Prefix: | omer_
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Balance Type: | na
Period Type: | instant

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- Definition Period of trading days before maturity within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature. + References No definition available. + Details
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