Deferred Royalty Obligation - Schedule of Deferred Royalty Obligation (Details) - USD ($) $ in Thousands	4 Months Ended	12 Months Ended
Dec. 31, 2024	Dec. 31, 2025
Deferred Royalty Acquired [Roll Forward]
Beginning acquired balance	$ 116,900	$ 120,613
Net accretion	3,713	950
Ending acquired balance	$ 120,613	$ 121,563

Amount of liability recognized arising from deferred royalty, expected to be settled beyond one year or the normal operating cycle, if longer.

No definition available.

Name:	coll_DeferredRoyaltyLiabilityNonCurrent
Namespace Prefix:	coll_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant