Consolidated Statements Of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (65,213)	$ 17,133	$ (76,339)	$ 51,395
Other comprehensive income (loss):
Foreign currency translation adjustment	927	(6,008)	(11,076)	(6,291)
Derivative financial instruments adjustment	2,213	(1,124)	(304)	(856)
Amortization of prior service costs and net gains or losses	2,931	2,078	8,793	6,236
Other comprehensive income (loss)	6,071	(5,054)	(2,587)	(911)
Comprehensive income (loss)	(59,142)	12,079	(78,926)	50,484
Amortization of prior service costs and net gains or losses, tax	836	593	2,507	1,778
Foreign currency translation adjustment, tax (benefit)	$ 19	$ (775)	$ 1,125	$ (775)