Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 205,301
Transition adjustment	(1,074,872)		$ (911,092)
Transition adjustment	(40,647)		$ (57,951)
Ending balance	(38,020)
Interest Rate Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(27,819)	$ 1,634
Losses arising during period	176	(40,148)
Amounts reclassified from accumulated other comprehensive loss	8,111	2,490
Net other comprehensive income (loss)	8,287	(37,658)
Ending balance	(19,532)	(36,024)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(26,623)	(23,916)
Losses arising during period	8,324	(1,106)
Amounts reclassified from accumulated other comprehensive loss	588	33
Net other comprehensive income (loss)	8,912	(1,073)
Ending balance	(17,711)	(24,989)
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	105	105
Net other comprehensive income (loss)	105	105
Ending balance	(3,404)	(3,614)
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)
Losses arising during period	8,500	(41,254)
Amounts reclassified from accumulated other comprehensive loss	8,804	2,628
Net other comprehensive income (loss)	17,304	(38,626)
Ending balance	$ (40,647)	(64,627)
AOCI Attributable to Parent [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transition adjustment		$ 2,158