Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 84,739	$ 72,382	$ 185,802	$ 123,539
Other comprehensive (loss) income, net of tax:
Changes in net prior service credit and actuarial losses	807	558	2,441	1,816
Change in fair value of derivatives	476	(51)	673	(526)
Foreign currency translation	(4,576)	14,369	(26,397)	52,303
Other comprehensive (loss) income	(3,293)	14,876	(23,283)	53,593
Comprehensive income	$ 81,446	$ 87,258	$ 162,519	$ 177,132