Shareholders' Equity - Net Change in Components of Accumulated Other Comprehensive Income (Loss) and the Related Tax Effects (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax amount	$ (29,576)	$ (132,361)	$ (16,953)	$ (365,138)
Other Comprehensive Income (Loss), Tax, Total	7,392	33,091	4,468	91,286
Other comprehensive income (loss), before reclassifications, net of tax amount			21,394	(274,118)
Reclassification from accumulated other comprehensive income, current period, net of tax amount			(8,909)	(266)
Other comprehensive income (loss), net of tax amount	(22,184)	(99,270)	(12,485)	(273,852)
Securities Available for Sale and Transferred Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, before tax amount	(26,963)	(114,317)	(16,062)	(314,517)
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, before tax amount	4,000	1,800	11,799	(31,451)
Other comprehensive income (loss), before tax amount	(22,963)	(112,517)	(4,263)	(345,968)
Other comprehensive income (loss), before reclassifications, tax (expense) benefit	6,740	28,580	4,246	78,630
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, tax (expense) benefit	(1,000)	(450)	(2,950)	7,863
Other Comprehensive Income (Loss), Tax, Total	5,740	28,130	1,296	86,493
Other comprehensive income (loss), before reclassifications, net of tax amount	(20,223)	(85,737)	(11,816)	(235,887)
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, net of tax amount	3,000	1,350	8,849	(23,588)
Other comprehensive income (loss), net of tax amount	(17,223)	(84,387)	(2,967)	(259,475)
Net Change in Prior Service Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	28	28	83	83
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(7)	(7)	(21)	(21)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	21	21	62	62
Recognized Net Loss Due to Lump Sum Settlements [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	0	0	25	0
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	0	0	(6)	0
Reclassification from accumulated other comprehensive income, current period, net of tax amount	0	0	19	0
Change in Net Actuarial Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	70	295	216	914
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(18)	(74)	(54)	(228)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	52	221	162	686
Pension and Other Postretirement Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	98	323	324	997
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(25)	(81)	(81)	(249)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	73	242	243	748
Cash Flow Hedge Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, before tax amount	(11,338)	(19,524)	(24,569)	(19,524)
Reclassification from accumulated other comprehensive income, current period, before tax amount	4,627	(643)	11,555	(643)
Other comprehensive income (loss), before tax amount	(6,711)	(20,167)	(13,014)	(20,167)
Other comprehensive income (loss), before reclassifications, tax (expense) benefit	2,834	4,881	6,142	4,881
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(1,157)	161	(2,889)	161
Other Comprehensive Income (Loss), Tax, Total	1,677	5,042	3,253	5,042
Other comprehensive income (loss), before reclassifications, net of tax amount	(8,504)	(14,643)	(18,427)	(14,643)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	3,470	(482)	8,666	(482)
Other comprehensive income (loss), net of tax amount	$ (5,034)	$ (15,125)	$ (9,761)	$ (15,125)