Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Product Warranty
Product warranty period	1 year
Changes in product warranty liability
Balance at the beginning of the period	$ 1,526	$ 1,428
Warranties issued during the period	1,080	647
Settlements made during the period	(566)	(467)
Changes in estimate of liability for pre-existing warranties during the period	123	12
Balance at the end of the period	2,163	1,620
Product warranty classification
Amount classified as current	1,909	1,496	1,352
Amount classified within other long-term liabilities	254	124
Total warranty liability	$ 2,163	$ 1,620