Accumulated Other Comprehensive Loss - Reclassification from Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reclassification Out Of Accumulated Other Comprehensive Loss
Unrealized losses on AFS securities before tax	$ (118)	$ (40)
Tax effect	(39,321)	(29,129)
Net income	115,710	87,268
Interest expense	(39,131)	(98,454)
Amortization of actuarial net loss	18,393	16,539
Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Out Of Accumulated Other Comprehensive Loss
Net income	(975)	(637)
Interest expense	(915)	(615)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Unrealized losses on AFS securities before tax	(59)	(40)
Tax effect	15	13
Net income	(44)	(27)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	264	177
Net income	(651)	(438)
Interest expense	(915)	(615)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	108	64
Net income	(280)	(172)
Amortization of actuarial net loss	$ (388)	$ (236)