REVENUE - Schedule of Disaggregated Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 59,225	$ 55,147	$ 57,203	$ 57,929	$ 42,599	$ 77,493	$ 63,274	$ 128,404	$ 229,504	$ 311,770	$ 380,724
Product sales, net
Disaggregation of Revenue [Line Items]
Total revenues	$ 28,917	$ 27,502	$ 25,937	$ 26,450	$ 29,339	$ 29,435	$ 26,838	44,354	108,806	129,966	379,880
Total neurology product sales, net
Disaggregation of Revenue [Line Items]
Total revenues									108,075	110,267	125,331
Gralise
Disaggregation of Revenue [Line Items]
Total revenues									63,124	58,077	77,034
CAMBIA
Disaggregation of Revenue [Line Items]
Total revenues									32,453	35,803	31,597
Zipsor
Disaggregation of Revenue [Line Items]
Total revenues									12,498	16,387	16,700
NUCYNTA products
Disaggregation of Revenue [Line Items]
Total revenues									927	18,944	239,539
Release of sales reserves								$ 12,500
Lazanda
Disaggregation of Revenue [Line Items]
Total revenues									(196)	755	15,010
Commercialization rights and facilitation services
Disaggregation of Revenue [Line Items]
Total revenues									118,614	100,038	0
Revenue from transfer of inventory
Disaggregation of Revenue [Line Items]
Total revenues									0	55,705	0
Royalties and milestone revenue
Disaggregation of Revenue [Line Items]
Total revenues									$ 2,084	$ 26,061	$ 844