Revenue (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Differentiation of revenue and cost of revenue
Revenue: Products	$ 71,523	$ 56,425	$ 127,853	$ 113,681
Revenue: Rentals	15,679	16,981	31,419	35,047
Revenue: Services	6,384	4,897	12,557	8,770
Total revenue	93,586	78,303	171,829	157,498
Cost of Revenue: Products	46,992	34,136	81,508	68,620
Cost of Revenue: Rentals	4,281	7,497	10,798	15,507
Cost of Revenue: Services	2,832	1,831	5,569	3,391
Cost of Revenue: Depreciation	1,887	1,814	3,730	3,504
Total cost of revenue	$ 55,992	$ 45,278	$ 101,605	$ 91,022