Accumulated Other Comprehensive (Loss) Income - Components of Accumulated Other Comprehensive (loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period			$ (95,921)
Total accumulated other comprehensive (loss) income, end of period	$ (4,842)		(4,842)
Changes in Fair Market Value of Derivatives
Changes in AOCI, Gross
Gross, beginning of the period	(529)	$ (4,239)	(1,038)	$ 659
Gross, gain (loss) recognized in OCI	(128)	525	568	(4,647)
Gross, gain (loss) reclassified from AOCI to earnings	(251)	656	(438)	930
Gross, ending balance	(908)	(3,058)	(908)	(3,058)
Changes in AOCI, Income tax benefit (expense)
Income tax benefit (expense), beginning of period	123	978	240	(150)
Income tax benefit (expense), gain (loss) recognized in OCI	29	(122)	(131)	1,059
Income tax benefit (expense), gain (loss) reclassified from AOCI to earnings	58	(150)	101	(203)
Income tax benefit (expense), ending of period	210	706	210	706
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	(406)	(3,261)	(798)	509
Gain (loss) recognized in OCI, net	(99)	403	437	(3,588)
(Gain) Loss reclassified from AOCI to earnings, net	(193)	506	(337)	727
Total accumulated other comprehensive (loss) income, end of period	(698)	(2,352)	(698)	(2,352)
Changes in Unrealized Pension Cost
Changes in AOCI, Gross
Gross, beginning of the period	(104,052)	(120,906)	(128,004)	(124,140)
Gross, gain (loss) recognized in OCI	(5,450)	0	(4,951)	0
Gross, gain (loss) reclassified from AOCI to earnings	106,622	1,606	130,075	4,840
Gross, ending balance	(2,880)	(119,300)	(2,880)	(119,300)
Changes in AOCI, Income tax benefit (expense)
Income tax benefit (expense), beginning of period	29,411	33,278	34,917	34,018
Income tax benefit (expense), gain (loss) recognized in OCI	1,254	0	1,139	0
Income tax benefit (expense), gain (loss) reclassified from AOCI to earnings	(29,896)	(367)	(35,287)	(1,107)
Income tax benefit (expense), ending of period	769	32,911	769	32,911
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	(74,641)	(87,628)	(93,087)	(90,122)
Gain (loss) recognized in OCI, net	(4,196)	0	(3,812)	0
(Gain) Loss reclassified from AOCI to earnings, net	76,726	1,239	94,788	3,733
Total accumulated other comprehensive (loss) income, end of period	(2,111)	(86,389)	(2,111)	(86,389)
Cumulative Translation Adjustment
Changes in AOCI, Gross
Gross, beginning of the period	(2,023)	(2,266)	(2,036)	(2,211)
Gross, gain (loss) recognized in OCI	(10)	99	3	44
Gross, gain (loss) reclassified from AOCI to earnings	0	0	0	0
Gross, ending balance	(2,033)	(2,167)	(2,033)	(2,167)
Changes in AOCI, Income tax benefit (expense)
Income tax benefit (expense), beginning of period				98
Income tax benefit (expense), gain (loss) recognized in OCI				(98)
Income tax benefit (expense), gain (loss) reclassified from AOCI to earnings				0
Income tax benefit (expense), ending of period		0		0
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period				(2,113)
Gain (loss) recognized in OCI, net				(54)
(Gain) Loss reclassified from AOCI to earnings, net				0
Total accumulated other comprehensive (loss) income, end of period		(2,167)		(2,167)
Accumulated Other Comprehensive Earnings/(Loss)
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	(77,070)	(93,155)	(95,921)	(91,726)
Gain (loss) recognized in OCI, net	(4,305)	502	(3,372)	(3,642)
(Gain) Loss reclassified from AOCI to earnings, net	76,533	1,745	94,451	4,460
Total accumulated other comprehensive (loss) income, end of period	$ (4,842)	$ (90,908)	$ (4,842)	$ (90,908)