Contingencies - Warranty Accrual Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance, beginning of year	$ 10,548	$ 10,183	$ 9,537
Additions charged to costs and expenses	10,820	15,950	14,284
Deductions	(11,170)	(15,513)	(13,059)
Other	389	(72)	(579)
Balance, end of year	$ 10,587	$ 10,548	$ 10,183