Other Assets and Liabilities - Other Non-Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Liabilities Disclosure [Abstract]
Provision for retirement indemnity	$ 1,303	$ 2,431	$ 2,170
Customer allowances	1,636	905
Unrecognized tax benefits	3,954	1,686	448	$ 0
Unrecognized tax benefits that would impact effective tax rate	3,349	1,565	$ 291
Other	191	374
Total	$ 7,084	$ 5,275