Revenue - Contract Costs (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)
Capitalized Contract Cost [Line Items]
Amortization of capitalized costs	$ 3,956	$ 7,942
Capitalized costs, net	5,913	5,913
Tooling [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	2,933	2,933
Design Costs [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	2,914	2,914
Other Capitalized Contract Cost [Member]
Capitalized Contract Cost [Line Items]
Capitalized costs, net	$ 66	$ 66