CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest [Abstract]
Net income	$ 21,388	$ 36,703	$ 41,788	$ 68,439
Unrealized (loss) gain on defined benefit plan, net of tax	(16,570)	1,020	(6,851)	(5,009)
Unrealized gain (loss) on swaps and collars, net of tax	817	503	(621)	(3,406)
Unrealized foreign currency gain (loss), net of tax	6,733	(6,900)	(2,881)	(1,964)
Comprehensive income	12,368	31,326	31,435	58,060
Less: Comprehensive income attributable to noncontrolling interest	(355)	(419)	(587)	(439)
Total comprehensive income attributable to common stockholders	$ 12,013	$ 30,907	$ 30,848	$ 57,621