Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 205,301
Transition adjustment	(1,016,953)		$ (911,092)
Transition adjustment	(51,851)		$ (57,951)
Ending balance	104,705
Interest Rate Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(27,819)	$ 1,634
Losses arising during period	602	(35,947)
Amounts reclassified from accumulated other comprehensive loss	4,001	(452)
Net other comprehensive income (loss)	4,603	(36,399)
Ending balance	(23,216)	(34,765)
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	1,436	(1,107)
Amounts reclassified from accumulated other comprehensive loss	8	17
Net other comprehensive income (loss)	1,444	(1,090)
Ending balance	(25,179)	(25,006)
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	53	52
Net other comprehensive income (loss)	53	52
Ending balance	(3,456)	(3,667)
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	2,038	(37,054)
Amounts reclassified from accumulated other comprehensive loss	4,062	(383)
Net other comprehensive income (loss)	6,100	(37,437)
Ending balance	$ (51,851)	(63,438)
AOCI Attributable to Parent [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transition adjustment		$ 2,158