REVENUE - Schedule of Disaggregated Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total revenues	$ 42,599	$ 77,493	$ 63,274	$ 128,404	$ 94,407	$ 95,413	$ 100,457	$ 90,447	$ 311,770	$ 380,724	$ 455,897
Product sales, net
Disaggregation of Revenue [Line Items]
Total revenues	$ 29,339	$ 29,435	$ 26,838	$ 44,354	$ 94,159	$ 95,204	$ 100,232	$ 90,285	129,966	379,880	455,066
Total neurology product sales, net
Disaggregation of Revenue [Line Items]
Total revenues									110,267	125,331	147,258
Gralise
Disaggregation of Revenue [Line Items]
Total revenues									58,077	77,034	88,446
CAMBIA
Disaggregation of Revenue [Line Items]
Total revenues									35,803	31,597	31,273
Zipsor
Disaggregation of Revenue [Line Items]
Total revenues									16,387	16,700	27,539
NUCYNTA products
Disaggregation of Revenue [Line Items]
Total revenues									18,944	239,539	281,261
Lazanda
Disaggregation of Revenue [Line Items]
Total revenues									755	15,010	26,547
Commercialization rights and facilitation services
Disaggregation of Revenue [Line Items]
Total revenues									100,038	0	0
Revenue from transfer of inventory
Disaggregation of Revenue [Line Items]
Total revenues									55,705	0	0
Royalties and milestone revenue
Disaggregation of Revenue [Line Items]
Total revenues									$ 26,061	$ 844	$ 831