Accumulated Other Comprehensive Loss - Reclassification from Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains (losses) on securities transactions, net	$ 787			$ (46)			$ 1,263	$ (127)
Tax effect	(42,424)			(38,891)			(124,626)	(101,486)
Net income	122,580	$ 120,512	$ 115,710	102,374	$ 95,601	$ 87,268	358,802	285,243
Interest expense	(27,775)			(54,257)			(99,647)	(218,677)
Amortization of actuarial net loss	20,400			18,251			56,721	53,312
Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Out Of Accumulated Other Comprehensive Loss
Net income	(409)			(1,334)			(2,272)	(1,866)
Interest expense	(1,044)			(1,586)			(2,708)	(1,763)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Unrealized gains (losses) on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains (losses) on securities transactions, net	825			(46)			663	(127)
Tax effect	(212)			10			(170)	33
Net income	613			(36)			493	(94)
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	301			459			780	506
Net income	(743)			(1,127)			(1,928)	(1,257)
Interest expense	(1,044)			(1,586)			(2,708)	(1,763)
Amounts Reclassified from Accumulated Other Comprehensive Loss | Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	109			63			326	184
Net income	(279)			(171)			(837)	(515)
Amortization of actuarial net loss	$ (388)			$ (234)			$ (1,163)	$ (699)