Accumulated Other Comprehensive (Loss) Income - Components of Accumulated Other Comprehensive (loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 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	(94,363)
Changes in Fair Market Value of Derivatives
Changes in AOCI, Gross
Gross, beginning of the period	(1,038)	$ 659
Gross, gain (loss) recognized in OCI	206	(5,422)
Gross, gain (loss) reclassified from AOCI to earnings	(45)	(281)
Gross, ending balance	(877)	(5,044)
Changes in AOCI, Income tax benefit (expense)
Income tax benefit (expense), beginning of period	240	(150)
Income tax benefit (expense), gain (loss) recognized in OCI	(47)	1,225
Income tax benefit (expense), gain (loss) reclassified from AOCI to earnings	10	64
Income tax benefit (expense), ending of period	203	1,139
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	(798)	509
Gain (loss) recognized in OCI, net	159	(4,197)
(Gain) Loss reclassified from AOCI to earnings, net	(35)	(217)
Total accumulated other comprehensive (loss) income, end of period	(674)	(3,905)
Changes in Unrealized Pension Cost
Changes in AOCI, Gross
Gross, beginning of the period	(128,004)	(124,140)
Gross, gain (loss) recognized in OCI	0	0
Gross, gain (loss) reclassified from AOCI to earnings	1,847	1,660
Gross, ending balance	(126,157)	(122,480)
Changes in AOCI, Income tax benefit (expense)
Income tax benefit (expense), beginning of period	34,917	34,018
Income tax benefit (expense), gain (loss) recognized in OCI	0	0
Income tax benefit (expense), gain (loss) reclassified from AOCI to earnings	(425)	(375)
Income tax benefit (expense), ending of period	34,492	33,643
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	(93,087)	(90,122)
Gain (loss) recognized in OCI, net	0	0
(Gain) Loss reclassified from AOCI to earnings, net	1,422	1,285
Total accumulated other comprehensive (loss) income, end of period	(91,665)	(88,837)
Cumulative Translation Adjustment
Changes in AOCI, Gross
Gross, beginning of the period	(2,036)	(2,211)
Gross, gain (loss) recognized in OCI	12	(41)
Gross, gain (loss) reclassified from AOCI to earnings	0	0
Gross, ending balance	(2,024)	(2,252)
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
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period		(2,113)
Gain (loss) recognized in OCI, net		(139)
(Gain) Loss reclassified from AOCI to earnings, net		0
Total accumulated other comprehensive (loss) income, end of period		(2,252)
Accumulated Other Comprehensive Earnings/(Loss)
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	(95,921)	(91,726)
Gain (loss) recognized in OCI, net	171	(4,336)
(Gain) Loss reclassified from AOCI to earnings, net	1,387	1,068
Total accumulated other comprehensive (loss) income, end of period	$ (94,363)	$ (94,994)