Liability Related to the Sale of Future Royalties and Milestones (Schedule of Liability Account) (Details) $ in Thousands	9 Months Ended
Sep. 30, 2025 USD ($)
Liability Related To Sale Of Future Royalties And Milestones [Abstract]
Liability related to sale of future royalties and milestones - beginning balance	$ 337,539
Non-cash royalty revenue	(77,535)
Non-cash interest expense recognized	36,243
Liability related to sale of future royalties and milestones - ending balance	296,247
Less: unamortized transaction costs	(1,074)
Liability related to sale of future royalties and milestones, net	$ 295,173

Liability related to sale of future royalties and milestones.

No definition available.

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Liability related to sale of future royalties and milestones including unamortized transaction costs.

No definition available.

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Period Type:	instant

Liability related to sale of future royalties and milestones net.

No definition available.

Name:	agen_LiabilityRelatedToSaleOfFutureRoyaltiesAndMilestonesNet
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Liability related to sale of future royalties, unamortized transaction costs.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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Non-cash interest expense related to sale of future royalties.

No definition available.

Name:	agen_NonCashInterestExpenseRelatedToSaleOfFutureRoyalties
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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Noncash royalty revenue recognized.

No definition available.

Name:	agen_NoncashRoyaltyRevenueRecognized
Namespace Prefix:	agen_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration