Consolidated Statements Of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustments, tax benefit	$ (404)	$ 195	$ 643
Unrealized (loss) gain on derivative instruments, tax (expense) benefit	186	936	(1,975)
Retirement benefit plan activity, tax benefit	$ 1,863	$ 0	$ 0