SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)
Product sales	$ 33,884	$ 30,584	$ 28,245	$ 21,506	$ 18,789	$ 16,278	$ 14,106	$ 9,129	$ 114,219	$ 58,302	$ 27,483
Total revenues	194,601	51,485	67,732	76,544	40,608	37,460	29,963	26,174	390,363	134,205	90,816
Gross margin on product sales	30,638	27,061	23,570	17,804	16,621	14,527	12,418	7,645
Income (loss) from operations	157,822	16,700	26,545	35,744	7,480	6,838	532	(5,533)	236,814	9,317	(30,353)
Net income (loss)	$ 94,623	$ 6,454	$ 12,746	$ 17,939	$ 41,801	$ 6,514	$ 478	$ (5,480)	$ 131,762	$ 43,313	$ (29,781)
Basic net income (loss) per share (in dollars per share)	$ 1.61	$ 0.11	$ 0.22	$ 0.31	$ 0.73	$ 0.11	$ 0.01	$ (0.10)	$ 2.26	$ 0.76	$ (0.53)
Diluted net income (loss) per share (in dollars per share)	$ 1.23	$ 0.11	$ 0.21	$ 0.30	$ 0.72	$ 0.11	$ 0.01	$ (0.10)	$ 2.05	$ 0.75	$ (0.53)