Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 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	832	925
Settlements made during the period	(978)	(705)
Changes in estimate of liability for pre-existing warranties during the period	79	(536)
Balance at the end of the period	1,361	1,485
Product warranty classification
Amount classified as current	1,326	1,419	1,316
Amount classified as long-term	35	66
Total Warranty liability	$ 1,361	$ 1,485