Accumulated Other Comprehensive (Loss) Income - Components of Accumulated Other Comprehensive (loss) Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	$ (91,726)
Total accumulated other comprehensive (loss) income, end of period	(95,921)	$ (91,726)
Changes in Fair Market Value of Derivatives
Changes in AOCI, Gross
Gross, beginning of the period	659	1,316
Gross, gain (loss) recognized in OCI	(3,015)	786
Gross, gain (loss) reclassified from AOCI to earnings	1,318	(1,443)
Gross, ending balance	(1,038)	659
Changes in AOCI, Income tax benefit (expense)
Income tax benefit (expense), beginning of period	(150)	(298)
Income tax benefit (expense), gain (loss) recognized in OCI	684	(178)
Income tax benefit (expense), gain (loss) reclassified from AOCI to earnings	(294)	326
Income tax benefit (expense), ending of period	240	(150)
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	509	1,018
Gain (loss) recognized in OCI, net	(2,331)	608
(Gain) Loss reclassified from AOCI to earnings, net	1,024	(1,117)
Total accumulated other comprehensive (loss) income, end of period	(798)	509
Changes in Unrealized Pension Cost
Changes in AOCI, Gross
Gross, beginning of the period	(124,140)	(132,454)
Gross, gain (loss) reclassified from AOCI to earnings	(3,864)	8,314
Gross, ending balance	(128,004)	(124,140)
Changes in AOCI, Income tax benefit (expense)
Income tax benefit (expense), beginning of period	34,018	35,893
Income tax benefit (expense), gain (loss) reclassified from AOCI to earnings	899	(1,875)
Income tax benefit (expense), ending of period	34,917	34,018
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	(90,122)	(96,561)
(Gain) Loss reclassified from AOCI to earnings, net	(2,965)	6,439
Total accumulated other comprehensive (loss) income, end of period	(93,087)	(90,122)
Cumulative Translation Adjustment
Changes in AOCI, Gross
Gross, beginning of the period	(2,211)	(2,291)
Gross, gain (loss) recognized in OCI	175	80
Gross, ending balance	(2,036)	(2,211)
Changes in AOCI, Income tax benefit (expense)
Income tax benefit (expense), beginning of period	98	95
Income tax benefit (expense), gain (loss) recognized in OCI	(98)	3
Income tax benefit (expense), ending of period		98
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	(2,113)	(2,196)
Gain (loss) recognized in OCI, net	77	83
Total accumulated other comprehensive (loss) income, end of period	(2,036)	(2,113)
Accumulated Other Comprehensive Loss
Changes in AOCI, Net
Total accumulated other comprehensive (loss) income, beginning of period	(91,726)	(97,739)
Gain (loss) recognized in OCI, net	(2,254)	691
(Gain) Loss reclassified from AOCI to earnings, net	(1,941)	5,322
Total accumulated other comprehensive (loss) income, end of period	$ (95,921)	$ (91,726)