EMPLOYEE BENEFITS (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
EMPLOYEE BENEFITS.
Requisite service period of employees to be eligible to participate in the 401(k) plan	3 months
Total expense for contributions made to 401(k) plan	$ 613	$ 44	$ 35

Represents the period that the employee is required to perform services from the date of employment, or anniversary thereof, in order to be eligible to participate in the defined contribution plan, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	coll_DefinedContributionPlanRequisiteServicePeriodForEligibilityToParticipateInPlan
Namespace Prefix:	coll_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration