REVENUE - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregated Revenue
Total revenues	$ 63,274			$ 191,678	$ 190,904
Calculated under Revenue Guidance in Effect before Topic 606
Disaggregated Revenue
Total revenues			$ 100,457
Product sales, net
Disaggregated Revenue
Total revenues	26,838			71,192	190,517
Product sales, net | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregated Revenue
Total revenues			100,232
Total neurology product sales, net
Disaggregated Revenue
Total revenues	25,892			51,881	60,461
Total neurology product sales, net | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregated Revenue
Total revenues			31,020
Gralise
Disaggregated Revenue
Total revenues	13,815			28,642	35,722
Gralise | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregated Revenue
Total revenues			18,122
CAMBIA
Disaggregated Revenue
Total revenues	8,089			14,505	15,685
CAMBIA | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregated Revenue
Total revenues			8,495
Zipsor
Disaggregated Revenue
Total revenues	3,988			8,734	9,054
Zipsor | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregated Revenue
Total revenues			4,403
NUCYNTA
Disaggregated Revenue
Total revenues	626			18,771	120,857
Reversal of sales reserves	600	$ 12,500
NUCYNTA | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregated Revenue
Total revenues			63,938
Lazanda
Disaggregated Revenue
Total revenues	320			540	9,199
Reversal of sales reserves	300
Lazanda | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregated Revenue
Total revenues			5,274
Commercialization rights and facilitation services
Disaggregated Revenue
Total revenues	31,179			59,274
Revenue from transfer of inventory
Disaggregated Revenue
Total revenues				55,705
Royalties and milestones
Disaggregated Revenue
Total revenues	$ 5,257			$ 5,507	$ 387
Royalties and milestones | Calculated under Revenue Guidance in Effect before Topic 606
Disaggregated Revenue
Total revenues			$ 225