Revenue - Contract Costs (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
Capitalized Contract Cost [Line Items]
Amortization of capitalized costs	$ 3,662	$ 3,956	$ 7,096	$ 7,942
Capitalized costs, net	8,148		8,148		$ 8,445
Tooling [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	5,732		5,732		6,155
Design Costs [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	2,416		2,416		2,285
Other Capitalized Contract Cost [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	$ 0		$ 0		$ 5