Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected Quarterly Financial Data (Unaudited)
Total revenues	$ 82,742	$ 82,258	$ 81,974	$ 80,894	$ 75,133	$ 73,554	$ 70,619	$ 68,152	$ 327,868	$ 287,458	$ 275,706
Product revenues	82,002	82,136	81,886	80,894	75,133	73,554	70,619	68,152	326,918	287,458	275,706
Cost of product revenues	13,180	13,062	15,221	15,800	14,269	13,718	13,033	12,762	57,263	53,782	48,742
Net loss	$ 1,352	$ (2,820)	$ (6,100)	$ (6,351)	$ (2,735)	$ (11,843)	$ (9,237)	$ (9,493)	$ (13,919)	$ (33,308)	$ (24,592)
Basic net income (loss) per share (in dollars per share)	$ 0.04	$ (0.08)	$ (0.18)	$ (0.19)
Diluted net income (loss) per share (in dollars per share)	$ 0.04	$ (0.08)	$ (0.18)	$ (0.19)
Basic and diluted net loss per share (in dollars per share)					$ (0.08)	$ (0.36)	$ (0.29)	$ (0.30)	$ (0.42)	$ (1.03)	$ (0.78)