Income Taxes (Details) - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits, Excluding Interest and Penalties - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 37,099	$ 25,911
Additions based on tax positions related to the current year	10,883	7,086
Additions for tax positions of prior years	24,299	6,443
Reductions for tax positions of prior years	(10,613)	(496)
Reductions for expiration of statutes	(1,368)	(1,006)
Settlements	(1,769)	(544)
Change in foreign currency exchange rates	1,738
Decrease in foreign currency exchange rates		(295)
Ending balance	$ 60,269	$ 37,099