Revenue (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Differentiation of revenue and cost of revenue
Revenue: Product	$ 224,777	$ 181,417	$ 95,021
Revenue: Rental	67,938	63,610	42,169
Revenue: Service	20,113	13,758	9,792
Total revenue	312,828	258,785	146,982
Cost of Revenue: Product	135,367	115,875	60,919
Cost of Revenue: Rental	30,618	25,971	20,355
Cost of Revenue: Service	8,051	4,997	3,517
Cost of Revenue: Depreciation	7,173	6,122	9,221
Total cost of revenue	$ 181,209	$ 152,965	$ 94,012