CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest [Abstract]
Net income	$ 36,703	$ 25,667	$ 68,439	$ 44,187
Unrealized gain (loss) on defined benefit plan, net of tax	1,020	7,266	(5,009)	7,701
Unrealized (loss) gain on swaps and collars, net of tax	503	927	(3,406)	3,275
Unrealized foreign currency loss, net of tax	(6,900)	(24,985)	(1,964)	(9,130)
Comprehensive income	31,326	8,875	58,060	46,033
Less: Comprehensive income attributable to noncontrolling interest	(419)	(599)	(439)	(593)
Total comprehensive income attributable to common stockholders	$ 30,907	$ 8,276	$ 57,621	$ 45,440