Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Product Warranty
Product warranty period	1 year
Changes in product warranty liability
Balance at the beginning of the period	$ 1,428	$ 1,801
Warranties issued during the period	647	457
Settlements made during the period	(467)	(399)
Changes in estimate of liability for pre-existing warranties during the period	12	(277)
Balance at the end of the period	1,620	1,582
Product warranty classification
Amount classified as current	1,496	1,539	1,316
Amount classified as long-term	124	43
Total warranty liability	$ 1,620	$ 1,582