Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss)
Balance	$ 286,096	$ 101,842	$ 30,553
Other comprehensive income (loss) before reclassifications	(29,913)	81,471	(101,811)
Amounts reclassified from accumulated other comprehensive income (loss)	30,925	27,347	64,023
Other comprehensive income (loss), net of tax	1,012	108,818	(37,788)
Balance	66,395	286,096	101,842
Cumulative Effect
Accumulated Other Comprehensive Income (Loss)
Balance	(21,900)
Balance		(21,900)
Cash flow hedges
Accumulated Other Comprehensive Income (Loss)
Balance	337	191	(406)
Other comprehensive income (loss) before reclassifications	(1,861)	278	(763)
Amounts reclassified from accumulated other comprehensive income (loss)	113	(132)	1,447
Other comprehensive income (loss), net of tax	(1,748)	146	684
Balance	(1,411)	337	191
Cash flow hedges | Cumulative Effect
Accumulated Other Comprehensive Income (Loss)
Balance			(87)
Cash flow hedges | Adjusted Balance
Accumulated Other Comprehensive Income (Loss)
Balance			(493)
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
Balance	2,849	(3,061)	1,597
Other comprehensive income (loss) before reclassifications	5,319	6,719	(2,579)
Amounts reclassified from accumulated other comprehensive income (loss)	(7,766)	(809)	(2,423)
Other comprehensive income (loss), net of tax	(2,447)	5,910	(5,002)
Balance	402	2,849	(3,061)
Available-for-sale securities | Cumulative Effect
Accumulated Other Comprehensive Income (Loss)
Balance			344
Available-for-sale securities | Adjusted Balance
Accumulated Other Comprehensive Income (Loss)
Balance			1,941
Pension and postretirement benefit plans
Accumulated Other Comprehensive Income (Loss)
Balance	(819,018)	(846,461)	(748,800)
Other comprehensive income (loss) before reclassifications	(70,623)	(845)	(46,170)
Amounts reclassified from accumulated other comprehensive income (loss)	38,578	28,288	64,999
Other comprehensive income (loss), net of tax	(32,045)	27,443	18,829
Balance	(851,063)	(819,018)	(846,461)
Pension and postretirement benefit plans | Cumulative Effect
Accumulated Other Comprehensive Income (Loss)
Balance			(116,490)
Pension and postretirement benefit plans | Adjusted Balance
Accumulated Other Comprehensive Income (Loss)
Balance			(865,290)
Foreign currency adjustments
Accumulated Other Comprehensive Income (Loss)
Balance	(24,311)	(99,630)	(47,331)
Other comprehensive income (loss) before reclassifications	37,252	75,319	(52,299)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Other comprehensive income (loss), net of tax	37,252	75,319	(52,299)
Balance	12,941	(24,311)	(99,630)
Foreign currency adjustments | Cumulative Effect
Accumulated Other Comprehensive Income (Loss)
Balance			0
Foreign currency adjustments | Adjusted Balance
Accumulated Other Comprehensive Income (Loss)
Balance			(47,331)
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss)
Balance	(840,143)	(948,961)	(794,940)
Balance	$ (839,131)	$ (840,143)	(948,961)
Accumulated other comprehensive loss | Cumulative Effect
Accumulated Other Comprehensive Income (Loss)
Balance			(116,233)
Accumulated other comprehensive loss | Adjusted Balance
Accumulated Other Comprehensive Income (Loss)
Balance			$ (911,173)