Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) product	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) segment product	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Segment information
Number of business segments in which the entity operates | segment									1
Number of products from which the majority of the entity's product revenues have been derived | product	1								1
Total revenues	$ 82,742	$ 82,258	$ 81,974	$ 80,894	$ 75,133	$ 73,554	$ 70,619	$ 68,152	$ 327,868	$ 287,458	$ 275,706
United States
Segment information
Total revenues									281,077	246,008	230,657
Outside of the United States
Segment information
Total revenues									$ 46,791	$ 41,450	$ 45,049