REVENUE - Revenue and Cash Collected from Commercialization Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues		$ 57,929	$ 128,404
Royalties and milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues		623	250
Revenue From Transfer Of Inventory From Commercialization Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues		0	55,705
Commercialization Agreement And Amended Commercialization Agreement | Collegium Pharmaceutical Inc
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from transfer of inventory			6,200
Proceeds received from Collegium		30,500	29,300
Commercialization Agreement And Amended Commercialization Agreement | Collegium Pharmaceutical Inc | Royalties and milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues		32,100	28,100
Net expense related to third-party royalty		$ 1,000
Performance Obligation Transfer Of Finished Goods | Collegium Pharmaceutical Inc | Revenue From Transfer Of Inventory From Commercialization Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues			55,700
NUCYNTA products | Commercialization Agreement | Collegium Pharmaceutical Inc
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment	$ 10,000		$ 10,000
Proceeds from transfer of inventory	$ 6,200