SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)
Product sales	$ 94,159	$ 95,204	$ 100,232	$ 90,285	$ 123,675	$ 110,303	$ 116,517	$ 104,571	$ 379,880	$ 455,066	$ 341,750
Total revenues	94,407	95,413	100,457	90,447	123,911	110,524	116,682	104,780	380,724	455,897	342,735
Gross margin on product sales	76,455	77,808	80,507	72,511	101,018	90,060	95,552	81,022
Loss from operations	(32,685)	1,238	(4,068)	(6,665)	17,904	1,258	9,661	(4,314)	(42,180)	24,509	(50,400)
Net loss	$ (33,104)	$ (15,992)	$ (26,659)	$ (26,741)	$ (44,368)	$ (12,894)	$ (10,541)	$ (20,917)	$ (102,496)	$ (88,720)	$ (75,738)
Basic net loss per share (in dollars per share)	$ (0.52)	$ (0.25)	$ (0.43)	$ (0.43)	$ (0.72)	$ (0.21)	$ (0.17)	$ (0.34)
Diluted net loss per share (in dollars per share)	$ (0.52)	$ (0.25)	$ (0.43)	$ (0.43)	$ (0.72)	$ (0.21)	$ (0.17)	$ (0.34)