REVENUE - Commercialization Agreement with Collegium (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 20,917	$ 57,929
Royalties and milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	407	623
Commercialization Agreement And Amended Commercialization Agreement \| Collegium Pharmaceutical Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	11,300
Contract asset, amortization	1,800
Commercialization Agreement And Amended Commercialization Agreement \| Collegium Pharmaceutical Inc \| Royalties and milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 13,100
Expense related to third-party royalties		$ 1,000

Revenue Recognition, Third-Party Royalty Net Expense

No definition available.

Name:	asrt_RevenueRecognitionThirdPartyRoyaltyNetExpense
Namespace Prefix:	asrt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

+ Details

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

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

+ Details

Name:	us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	srt_ProductOrServiceAxis=asrt_RoyaltiesAndMilestonesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=asrt_CommercializationAgreementAndAmendedCommercializationAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=asrt_CollegiumPharmaceuticalIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: