Revenue (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Differentiation of revenue and cost of revenue
Revenue: Product	$ 56,621	$ 54,841	$ 170,302	$ 128,508
Revenue: Rental	16,374	16,632	51,420	45,590
Revenue: Service	5,633	3,585	14,404	9,783
Total revenue	78,628	75,058	236,126	183,881
Cost of Revenue: Product	32,910	34,686	101,528	82,734
Cost of Revenue: Rental	7,806	6,778	23,312	18,984
Cost of Revenue: Service	2,271	1,302	5,665	3,554
Cost of Revenue: Depreciation	1,798	1,575	5,302	4,503
Total cost of revenue	$ 44,785	$ 44,341	$ 135,807	$ 109,775