Revenue (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Differentiation of revenue and cost of revenue
Revenue: Products	$ 82,406	$ 56,330
Revenue: Rentals	13,923	15,740
Revenue: Services	6,246	6,173
Total revenue	102,575	78,243
Cost of Revenue: Products	47,732	34,516
Cost of Revenue: Rentals	6,513	6,517
Cost of Revenue: Services	2,715	2,737
Cost of Revenue: Depreciation	1,934	1,843
Total cost of revenue	$ 58,894	$ 45,613