Commitments and Contingencies (Warranty activity) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Letters of credit outstanding	$ 2,200		$ 2,200
Accrued Expenses
Movement in Standard Product Warranty Accrual [Roll Forward]
Warranty accrual, beginning of period	2,980	$ 2,083
Warranties issued	653	404
Settlements	(862)	(247)
Warranty accrual, end of period	2,627	$ 2,236
Performance Bonds
Product Warranty Liability [Line Items]
Amount of performance bonds outstanding	$ 5,400		$ 5,300