Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance January 1	$ 3,775	$ 7,228	$ 3,619
Gross increase due to non-U.S. acquisitions	0	0	3,772
Gross increases for tax positions of prior years	537	201	1,256
Gross decreases for tax positions of prior years	(587)	(93)	0
Settlements	(604)	(2,014)	(667)
Lapse of statute of limitations	(399)	(1,547)	(752)
Ending balance December 31	$ 2,722	$ 3,775	$ 7,228