Warranty Accrual Activity (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at beginning of period	$ 3,841	$ 2,638
Charged to cost of revenues	3,690	1,993
Actual warranty expenditures	(2,503)	(1,801)
Balance at end of period	$ 5,028	$ 2,830