Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 205,301
Transition adjustment	(1,083,411)		$ (911,092)
Transition adjustment	(36,574)		$ (57,951)
Ending balance	(39,232)
Interest Rate Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(27,819)	$ 1,634
Gains (losses) arising during period	(370)	(39,965)
Amounts reclassified from accumulated other comprehensive loss	12,298	6,479
Net other comprehensive income (loss)	11,928	(33,486)
Ending balance	(15,891)	(31,852)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(26,623)	(23,916)
Gains (losses) arising during period	8,324	(11,167)
Amounts reclassified from accumulated other comprehensive loss	966	1,444
Net other comprehensive income (loss)	9,290	(9,723)
Ending balance	(17,333)	(33,639)
Accumulated Other-than-Temporary Impairment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(3,509)	(5,877)
Amounts reclassified from accumulated other comprehensive loss	159	158
Net other comprehensive income (loss)	159	158
Ending balance	(3,350)	(3,561)
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	(57,951)	(28,159)
Gains (losses) arising during period	7,954	(51,132)
Amounts reclassified from accumulated other comprehensive loss	13,423	8,081
Net other comprehensive income (loss)	21,377	(43,051)
Ending balance	$ (36,574)	(69,052)
AOCI Attributable to Parent [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transition adjustment		$ 2,158