Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 644,729
Transition adjustment	(831,265)				$ (495,514)
Transition adjustment	(69,052)				$ (28,159)
Ending balance	271,926
Cumulative Effect, Period of Adoption, Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transition adjustment			$ (5,300)
Transition adjustment				$ 2,200
Interest Rate Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,634
Losses arising during period	(39,965)	$ (3,789)
Amounts reclassified from accumulated other comprehensive loss	6,479	(1,197)
Net other comprehensive income (loss)	(33,486)	(4,986)
Ending balance	(31,852)	(4,986)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(23,916)	(21,814)
Losses arising during period	(11,167)	(5,164)
Amounts reclassified from accumulated other comprehensive loss	1,444	1,635
Income tax benefit		(880)
Net other comprehensive income (loss)	(9,723)	(2,649)
Ending balance	(33,639)	(27,170)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transition adjustment		(2,707)
Accumulated Other-than-Temporary Impairment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(5,877)	(6,210)
Amounts reclassified from accumulated other comprehensive loss	158	249
Net other comprehensive income (loss)	158	249
Ending balance	(3,561)	(5,961)
Accumulated Other-than-Temporary Impairment Attributable to Parent [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transition adjustment	2,158
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(28,159)	(28,024)
Losses arising during period	(51,132)	(8,953)
Amounts reclassified from accumulated other comprehensive loss	8,081	687
Income tax benefit		(880)
Net other comprehensive income (loss)	(43,051)	(7,386)
Ending balance	(69,052)	(38,117)
AOCI Attributable to Parent [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transition adjustment	$ 2,158	$ (2,707)