SELECTED QUARTERLY FINANCIAL DATA (UNADUITED) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ 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
Revenue, Initial Application Period Cumulative Effect Transition [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
Gross margin on product sales	28,635	26,460	24,085	32,310	76,455	77,808	80,507	72,511
(Loss) income from operations	(13,082)	9,628	(4,225)	51,338	(32,685)	1,238	(4,068)	(6,665)	43,659	(42,180)	24,509
Net income (loss)	$ (24,138)	$ 48,270	$ (21,048)	$ 33,824	$ (33,104)	$ (15,992)	$ (26,659)	$ (26,741)	$ 36,908	$ (102,496)	$ (88,720)
Basic net loss per share (in dollars per share)	$ (0.38)	$ 0.76	$ (0.33)	$ 0.53	$ (0.52)	$ (0.25)	$ (0.43)	$ (0.43)	$ 0.58	$ (1.63)	$ (1.45)
Diluted net loss per share (in dollars per share)	$ (0.38)	$ 0.65	$ (0.33)	$ 0.48	$ (0.52)	$ (0.25)	$ (0.43)	$ (0.43)	$ 0.57	$ (1.63)	$ (1.45)
Product sales, net
Revenue, Initial Application Period Cumulative Effect Transition [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