Revenue - Contract Costs (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Capitalized Contract Cost [Line Items]
Amortization of capitalized costs	$ 3,986
Capitalized costs, net	7,370
Tooling [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	3,937
Design Costs [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	3,340
Other Capitalized Contract Cost [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	$ 93