Commitments and Contingencies (Warranty activity) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Letters of Credit Outstanding, Amount	$ 2,000		$ 2,000		$ 2,200
Accrued Expenses
Movement in Standard Product Warranty Accrual [Roll Forward]
Warranty accrual, beginning of period	2,627	$ 2,236
Warranties issued	768	709	1,421	$ 1,113
Settlements	(544)	(393)	(1,406)	(640)
Warranty accrual, end of period	2,898	$ 2,539	2,898	$ 2,539
Performance Bonds
Product Warranty Liability [Line Items]
Amount of performance bonds outstanding	$ 4,700		$ 4,700		$ 5,300