Nature of Business and Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP). These unaudited condensed consolidated financial statements include all adjustments, which include normal recurring adjustments, necessary for the fair presentation of the Company’s financial position. These unaudited interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2023, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates and changes in these estimates are recorded when known. The unaudited condensed consolidated financial statements include the accounts of the Company and our wholly owned subsidiary, Aptevo Research and Development LLC. All intercompany balances and transactions have been eliminated.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires estimates and assumptions that affect the reported amounts of assets and liabilities, revenues and expenses, and related disclosures of contingent liabilities in the unaudited condensed financial statements and accompanying notes. Estimates are used for, but not limited to, clinical accruals, useful lives of equipment, commitments and contingencies, stock-based compensation, and incremental borrowing rate (IBR) used for our lease. Given the global economic and geopolitical climate, these estimates are becoming more challenging, and actual results could differ materially from those estimates.
Gain Related to Sale of Nonfinancial Asset	Gain Related to Sale of Nonfinancial Asset to XOMA (US) LLC On March 29, 2023, we entered into and closed a payment interest purchase agreement (the “Purchase Agreement”) with XOMA (US) LLC (“XOMA”) pursuant to which we sold to XOMA our right, title and interest in all of the deferred payments and a portion of the milestone payments from Medexus pursuant to our LLC Purchase Agreement with Medexus, dated February 28, 2020 (the "LLC Agreement"). Under the terms of the Purchase Agreement, we received $9.6 million at closing (the “Closing Payment”) and an additional post-closing payment of $0.05. We accounted for the $9.6 million Closing Payment and the $0.05 million post-closing payment from XOMA as other income in accordance with Accounting Standards Codification ("ASC") 610-20 Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets in the first quarter of 2023. Contractual rights sold to XOMA represent an intangible asset under ASC 610-20 Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets for which XOMA bears all benefit and Aptevo has no obligations going forward. The Company will continue to account for its portion of future milestones under our LLC Purchase Agreement with Medexus as contingent consideration under ASC 450-30 Gain Contingencies and will record income when proceeds are received.
Other Significant Accounting Policies	Other Significant Accounting Policies Our other significant accounting policies were reported in our Annual Report on Form 10-K for the year ended December 31, 2023 that was filed with the SEC on March 5, 2024. Our other significant accounting policies have not changed materially from the policies previously reported.

Nature of Business and Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2024

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP). These unaudited condensed consolidated financial statements include all adjustments, which include normal recurring adjustments, necessary for the fair presentation of the Company’s financial position. These unaudited interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2023, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023.

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates and changes in these estimates are recorded when known.

The unaudited condensed consolidated financial statements include the accounts of the Company and our wholly owned subsidiary, Aptevo Research and Development LLC. All intercompany balances and transactions have been eliminated.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires estimates and assumptions that affect the reported amounts of assets and liabilities, revenues and expenses, and related disclosures of contingent liabilities in the unaudited condensed financial statements and accompanying notes. Estimates are used for, but not limited to, clinical accruals, useful lives of equipment, commitments and contingencies, stock-based compensation, and incremental borrowing rate (IBR) used for our lease. Given the global economic and geopolitical climate, these estimates are becoming more challenging, and actual results could differ materially from those estimates.

Gain Related to Sale of Nonfinancial Asset to XOMA (US) LLC

On March 29, 2023, we entered into and closed a payment interest purchase agreement (the “Purchase Agreement”) with XOMA (US) LLC (“XOMA”) pursuant to which we sold to XOMA our right, title and interest in all of the deferred payments and a portion of the milestone payments from Medexus pursuant to our LLC Purchase Agreement with Medexus, dated February 28, 2020 (the "LLC Agreement"). Under the terms of the Purchase Agreement, we received $9.6 million at closing (the “Closing Payment”) and an additional post-closing payment of $0.05.

We accounted for the $9.6 million Closing Payment and the $0.05 million post-closing payment from XOMA as other income in accordance with Accounting Standards Codification ("ASC") 610-20 Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets in the first quarter of 2023. Contractual rights sold to XOMA represent an intangible asset under ASC 610-20 Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets for which XOMA bears all benefit and Aptevo has no obligations going forward. The Company will continue to account for its portion of future milestones under our LLC Purchase Agreement with Medexus as contingent consideration under ASC 450-30 Gain Contingencies and will record income when proceeds are received.

Other Significant Accounting Policies

Our other significant accounting policies were reported in our Annual Report on Form 10-K for the year ended December 31, 2023 that was filed with the SEC on March 5, 2024. Our other significant accounting policies have not changed materially from the policies previously reported.