Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014 product	Jun. 30, 2013	Jun. 30, 2014 segment product	Jun. 30, 2013
Segment Information
Number of business segments in which the entity operates			1
Number of products from which the majority of the entity's product revenues have been derived	1		1
Segment information
Total revenues	$ 70,477	$ 63,691	$ 137,479	$ 126,785
United States
Segment information
Total revenues	58,617	54,520	114,085	109,083
Outside of the United States
Segment information
Total revenues	$ 11,860	$ 9,171	$ 23,394	$ 17,702