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)
Total revenues	$ 75,133	$ 73,554	$ 70,619	$ 68,152	$ 69,126	$ 69,101	$ 70,477	$ 67,002	$ 287,458	$ 275,706	$ 261,595
Product revenues	75,133	73,554	70,619	68,152	69,126	69,101	70,477	67,002	287,458	275,706	259,192
Cost of product revenues	14,269	13,718	13,033	12,762	12,501	11,979	12,207	12,055	53,782	48,742	42,100
Net loss	$ (2,735)	$ (11,843)	$ (9,237)	$ (9,493)	$ (6,267)	$ (6,262)	$ (4,618)	$ (7,445)	$ (33,308)	$ (24,592)	$ (12,757)
Basic and diluted net loss per share (in dollars per share)	$ (0.08)	$ (0.36)	$ (0.29)	$ (0.30)	$ (0.20)	$ (0.20)	$ (0.15)	$ (0.24)	$ (1.03)	$ (0.78)	$ (0.42)