Revenue (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Differentiation of revenue and cost of revenue
Revenue: Products	$ 56,330	$ 57,256
Revenue: Rentals	15,740	18,066
Revenue: Services	6,173	3,873
Total revenue	78,243	79,195
Cost of Revenue: Products	34,516	34,485
Cost of Revenue: Rentals	6,517	8,013
Cost of Revenue: Services	2,737	1,556
Cost of Revenue: Depreciation	1,843	1,690
Total cost of revenue	$ 45,613	$ 45,744