Revenue (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Differentiation of Revenue and Cost of Revenue
Revenue: Product	$ 55,156	$ 37,040	$ 110,924	$ 72,012
Revenue: Rentals	16,981	14,823	35,047	28,958
Revenue: Service	6,166	4,055	11,527	7,853
Total revenue	78,303	55,918	157,498	108,823
Cost of revenue: Product	32,030	23,438	64,427	45,105
Cost of revenue: Rental	7,784	6,401	16,359	12,882
Cost of revenue: Service	3,650	2,355	6,732	4,520
Cost of revenue: Depreciation	1,814	1,480	3,504	2,927
Total cost of revenue	$ 45,278	$ 33,674	$ 91,022	$ 65,434