SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)
Product sales	$ 111,059	$ 104,726	$ 94,295	$ 31,670	$ 33,884	$ 30,584	$ 28,245	$ 21,506	$ 341,750	$ 114,219	$ 58,302
Total revenues	111,172	104,856	94,504	32,203	194,601	51,485	67,732	76,544	342,735	390,363	134,205
Gross margin on product sales	90,052	83,812	71,430	28,558	30,638	27,061	23,570	17,804
Income (loss) from operations	(26,572)	3,235	(17,214)	(9,849)	157,822	16,700	26,545	35,744	(50,400)	236,814	9,317
Net income (loss)	$ (30,677)	$ (11,785)	$ (21,653)	$ (11,633)	$ 94,623	$ 6,454	$ 12,746	$ 17,939	$ (75,738)	$ 131,762	$ 43,313
Basic net income (loss) per share (in dollars per share)	$ (0.51)	$ (0.20)	$ (0.36)	$ (0.20)	$ 1.61	$ 0.11	$ 0.22	$ 0.31	$ (1.26)	$ 2.26	$ 0.76
Diluted net income (loss) per share (in dollars per share)	$ (0.51)	$ (0.20)	$ (0.36)	$ (0.20)	$ 1.23	$ 0.11	$ 0.21	$ 0.30	$ (1.26)	$ 2.05	$ 0.75