Revenue (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Differentiation of revenue and cost of revenue
Revenue: Products	$ 76,376	$ 56,621	$ 204,229	$ 170,302
Revenue: Rentals	15,375	16,374	46,794	51,420
Revenue: Services	6,637	5,633	19,194	14,404
Total revenue	98,388	78,628	270,217	236,126
Cost of Revenue: Products	50,367	32,910	131,875	101,528
Cost of Revenue: Rentals	6,868	7,806	17,666	23,312
Cost of Revenue: Services	1,610	2,271	7,179	5,665
Cost of Revenue: Depreciation	2,041	1,798	5,771	5,302
Total cost of revenue	$ 60,886	$ 44,785	$ 162,491	$ 135,807