Income Taxes - Reconciliation Between the Effective and Nominal Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income before taxes	$ 120,458	$ 71,793	$ 64,474
Theoretical group tax-rates	34.43%	34.43%	34.43%
Nominal tax expense	$ (41,474)	$ (24,718)	$ (22,198)
Increase / decrease in tax expense arising from:
Research tax credit	1,701	1,352	1,743
Net effect of shared based compensation	(8,957)	2,048	3,419
Other permanent differences	(3,518)	(804)	(2,245)
Non recognition of deferred tax assets related to tax losses and temporary differences	(7,738)	(7,662)	(3,546)
Utilization or recognition of previously unrecognized tax losses	13,366	12,264	276
French CVAE included in income taxes	(3,165)	(3,052)	(2,467)
Special tax deductions	20,022	12,545	8,984
Effect of different tax rates	(1,108)	(1,046)	(1,019)
Other differences	(2,258)	(444)	(525)
Provision for income tax	$ (33,129)	$ (9,517)	$ (17,578)
Effective tax rate	27.50%	13.30%	27.30%