Commitments and Contingencies (Warranty activity) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Letters of Credit Outstanding, Amount	$ 3,300		$ 3,300		$ 2,200
Movement in Standard Product Warranty Accrual [Roll Forward]
Standard Product Warranty Accrual, Increase (Decrease) for Preexisting Warranties	169	$ 34	72	$ 17
Accrued Expenses
Movement in Standard Product Warranty Accrual [Roll Forward]
Warranty accrual, beginning of period	2,898	2,539	2,980	2,083
Warranties issued	930	532	2,351	1,645
Settlements	(639)	(455)	(2,045)	(1,095)
Warranty accrual, end of period	3,358	$ 2,650	3,358	$ 2,650
Performance Bonds
Product Warranty Liability [Line Items]
Amount of performance bonds outstanding	$ 5,200		$ 5,200		$ 5,300