Revenue - Contract Costs (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
Capitalized Contract Cost [Line Items]
Amortization of capitalized costs	$ 3,506	$ 3,606	$ 10,614	$ 11,548
Capitalized costs, net	8,672		8,672		$ 8,445
Tooling [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	6,231		6,231		6,155
Design Costs [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	2,441		2,441		2,285
Other Capitalized Contract Cost [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	$ 0		$ 0		$ 5