Product Warranty (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Product Warranty
Product warranty period	1 year
Changes in standard product warranty liability
Balance at January 1 (beginning of year)	$ 3,244	$ 5,091
Warranties issued during the period	1,385	954
Settlements made during the period	(950)	(1,475)
Changes in estimate of liability for pre-existing warranties during the period	126	89
Balance at March 31 (end of period)	3,805	4,659
Product warranty classification
Amount classified as current			$ 3,431	$ 2,759	$ 4,319
Amount classified as long-term			374		340
Total warranty liability	$ 3,805	$ 4,659	$ 3,805	$ 3,244	$ 4,659