Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 172,492	$ 212,948	$ 455,361
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments, net of tax benefit (expense) of ($404), $195 and $643	41,691	(19,773)	(38,571)
Unrealized gain (loss) on derivative instruments, net of tax benefit (expense) of $186, $936 and ($1,975)	(330)	(1,572)	3,320
Retirement benefit plan activity, net of tax benefit of $1,863, $0 and $0	(3,153)	0	0
Comprehensive income	$ 210,700	$ 191,603	$ 420,110