Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Product Warranty
Product warranty period	1 year
Changes in product warranty liability
Balance at the beginning of the period	$ 1,801	$ 3,697
Warranties issued during the period	925	1,657
Settlements made during the period	(705)	(1,873)
Changes in estimate of liability for pre-existing warranties during the period	(536)	(770)
Balance at the end of the period	1,485	2,711
Product warranty classification
Amount classified as current	1,419	2,589	1,700
Amount classified as long-term	66	122
Total warranty liability	$ 1,485	$ 2,711