Deferred Royalty Obligation -Narrative (Details) $ in Thousands	6 Months Ended
Jun. 30, 2025 USD ($)
Deferred Royalty Obligation
Effective interest rate	11.83%
Interest expense on deferred royalty obligation	$ 7,137
Net accretion for deferred royalty obligation	2,014
Total royalty payments	$ 4,147
Net sales prior to July 1, 2025
Deferred Royalty Obligation
Royalty rate	7.40%
Net sales after July 1, 2025 and up to March, 2032.
Deferred Royalty Obligation
Royalty rate	9.70%

Line items represent information about deferred royalty liability.

No definition available.

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Period Type:	duration

Effective interest rate for the deferred royalty obligations.

No definition available.

Name:	coll_DeferredRoyaltyObligationInterestRateEffectivePercentage
Namespace Prefix:	coll_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Amount of interest expense recognized during the period towards deferred royalty liability obligation.

No definition available.

Name:	coll_InterestExpenseOnDeferredRoyaltyLiability
Namespace Prefix:	coll_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of net accretion from deferred royalty obligation.

No definition available.

Name:	coll_NetAccretionForDeferredRoyaltyObligation
Namespace Prefix:	coll_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of deferred royalty obligation paid during the period.

No definition available.

Name:	coll_PaymentOfDeferredRoyaltyObligation
Namespace Prefix:	coll_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Percentage of royalty amount agreed to be paid upon net sales.

No definition available.

Name:	srt_StatementScenarioAxis=coll_NetSalesPriorToJuly12025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_StatementScenarioAxis=coll_NetSalesPriorAfterJuly12025AndUpToMarch2032Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: