Revenue (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Differentiation of revenue and cost of revenue
Revenue: Products	$ 92,708	$ 76,376	$ 257,415	$ 204,229
Revenue: Rentals	16,966	15,375	45,954	46,794
Revenue: Services	7,087	6,637	21,284	19,194
Total revenue	116,761	98,388	324,653	270,217
Cost of Revenue: Products	57,315	50,367	155,048	131,875
Cost of Revenue: Rentals	8,272	6,868	22,444	17,666
Cost of Revenue: Services	3,074	1,610	9,042	7,179
Cost of Revenue: Depreciation	2,022	2,041	6,051	5,771
Total cost of revenue	$ 70,683	$ 60,886	$ 192,585	$ 162,491