Product Warranty (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Product Warranty
Product warranty period	1 year
Changes in standard product warranty liability
Balance at January 1 (beginning of year)	$ 3,244	$ 5,091	$ 4,502
Warranties issued during the period	5,005	3,615	5,421
Settlements made during the period	(4,270)	(5,548)	(5,903)
Changes in estimate of liability for pre-existing warranties during the period	633	86	1,071
Balance at December 31 (end of period)	4,612	3,244	5,091
Product warranty classification
Amount classified as current				$ 4,280	$ 2,759	$ 4,819
Amount classified as long-term				332	485	272
Total warranty liability	$ 3,244	$ 3,244	$ 4,502	$ 4,612	$ 3,244	$ 5,091