Revenue (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Differentiation of revenue and cost of revenue
Revenue: Products	$ 82,302	$ 71,523	$ 164,707	$ 127,853
Revenue: Rentals	15,065	15,679	28,989	31,419
Revenue: Services	7,951	6,384	14,197	12,557
Total revenue	105,318	93,586	207,893	171,829
Cost of Revenue: Products	49,995	46,992	97,731	81,508
Cost of Revenue: Rentals	7,654	4,281	14,165	10,798
Cost of Revenue: Services	3,265	2,832	5,978	5,569
Cost of Revenue: Depreciation	2,094	1,887	4,029	3,730
Total cost of revenue	$ 63,008	$ 55,992	$ 121,903	$ 101,605