Revenue (Details) (USD $) In Thousands, 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
Revenue:
Products									$ 354,356	$ 282,639	$ 224,777
Rentals									65,549	62,042	67,938
Services									29,252	26,384	20,113
Total revenues	124,503	116,761	105,318	102,575	100,848	98,388	93,586	78,243	449,157	371,065	312,828
Cost of Revenue:
Products									214,417	180,800	135,367
Rentals									31,285	24,987	30,618
Services									12,385	9,916	8,051
Depreciation									8,111	7,835	7,173
Total cost of revenue									$ 266,198	$ 223,538	$ 181,209