Represents the advance written notice termination period.

No definition available.

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

- Definition

Rent-free portion of the term of the lessee's leasing arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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

- Definition

The number of renewal periods available under the lease.

+ References

No definition available.

+ Details

Name:	coll_NumberOfRenewalPeriodsOperatingLease
Namespace Prefix:	coll_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of operating lease increased annually.

+ References

No definition available.

+ Details

Name:	coll_OperatingLeaseAnnualBaseRentIncreasePercentage
Namespace Prefix:	coll_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Cost of operating lease per rentable square foot.

+ References

No definition available.

+ Details

Name:	coll_OperatingLeaseAnnualInitialBaseRentPerSquareFoot
Namespace Prefix:	coll_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LesseeLeaseDescriptionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseRenewalTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=coll_OperatingLeaseArrangementWithContractManufacturingOrganizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=coll_OperatingLeaseArrangementForVehiclesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=coll_StoughtonMassachusettsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=coll_CantonMassachusettsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Leases - Operating Lease Arrangements (Details) $ in Thousands	1 Months Ended
	Mar. 31, 2018 USD ($) ft² item $ / ft²	Jan. 31, 2016 ft²	Dec. 31, 2018
CMO
Lessee, Lease, Description [Line Items]
Square of feet of space		3,267
Term of lease extension option		2 years
Advance written notice termination period		2 years
Vehicle leases
Lessee, Lease, Description [Line Items]
Lease term			12 months
Stoughton, Massachusetts
Lessee, Lease, Description [Line Items]
Rent-free term	4 months
Square of feet of space	50,678
Lease term	10 years
Number of renewal periods \| item	2
Term of lease extension option	5 years
Base rent \| $	$ 1,214
Annual base rent per rentable square foot \| $ / ft²	23.95
Canton, Massachusetts
Lessee, Lease, Description [Line Items]
Square of feet of space	9,660
Term of lease extension option	5 years
Maximum \| Stoughton, Massachusetts
Lessee, Lease, Description [Line Items]
Increase in annual base rent	3.10%
Minimum \| Stoughton, Massachusetts
Lessee, Lease, Description [Line Items]
Increase in annual base rent	2.50%