Revenue

The Company differentiates revenue and cost of revenue based on whether the source of revenue is attributable to products, rentals or services. Revenue and cost of revenue by source are as follows (in thousands):



	Year ended December 31,
	2012		2011		2010
Revenue:
Products	$	224,777	$	181,417	$	95,021
Rentals	67,938		63,610		42,169
Services	20,113		13,758		9,792
	$	312,828	$	258,785	$	146,982
Cost of Revenue:
Products	$	135,367	$	115,875	$	60,919
Rentals	30,618		25,971		20,355
Services	8,051		4,997		3,517
Depreciation	7,173		6,122		9,221
	$	181,209	$	152,965	$	94,012