CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest [Abstract]
Net income	$ 38,122	$ 31,210	$ 106,561	$ 75,397
Unrealized (loss) gain on defined benefit plan, net of tax	(6,553)	(493)	(11,562)	7,207
Unrealized gain (loss) on swaps and collars, net of tax	259	378	(3,146)	3,653
Unrealized foreign currency loss, net of tax	(9,186)	(9,849)	(11,151)	(18,978)
Comprehensive income	22,642	21,246	80,702	67,279
Less: Comprehensive income attributable to noncontrolling interest	(62)	(302)	(501)	(895)
Total comprehensive income attributable to common stockholders	$ 22,580	$ 20,944	$ 80,201	$ 66,384