Additional Financial Information Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Changes in warranty and after-sale costs reserve
Balance at beginning of period	$ 2,548	$ 3,561	$ 2,779	$ 3,133
Net additions charged to earnings	1,231	398	1,983	1,238
Adjustments to pre-existing warranties	440	610	46	863
Costs incurred	(1,155)	(1,056)	(1,744)	(1,721)
Balance at end of period	$ 3,064	$ 3,513	$ 3,064	$ 3,513