Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Product Warranty
Product warranty period	1 year
Changes in product warranty liability
Balance at the beginning of the period	$ 3,697	$ 2,713
Warranties issued during the period	1,657	2,711
Settlements made during the period	(1,873)	(2,214)
Changes in estimate of liability for pre-existing warranties during the period	(770)	1,149
Balance at the end of the period	2,711	4,359
Product warranty classification
Amount classified as current	2,589	4,131	3,556
Amount classified as other long-term liabilities	122	228
Total warranty liability	$ 2,711	$ 4,359