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, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax amount	$ 14,812	$ 83,349	$ 85,705	$ 254,237
Other Comprehensive Income (Loss), Tax, Total	(3,703)	(20,837)	(21,426)	(63,559)
Other comprehensive income (loss), before reclassifications, net of tax amount			58,318	42,444
Reclassification from accumulated other comprehensive income, current period, net of tax amount			5,961	148,234
Other comprehensive income (loss), net of tax amount	11,109	62,512	64,279	190,678
Securities Available for Sale and Transferred Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, before tax amount	9,714	55,892	56,305	47,579
Reclassification from accumulated other comprehensive income, current period, before tax amount	0	0	0	182,792
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, before tax amount	3,422	3,688	10,297	11,020
Other comprehensive income (loss), before tax amount	13,136	59,580	66,602	241,391
Other comprehensive income (loss), before reclassifications, tax (expense) benefit	(2,428)	(13,973)	(14,076)	(11,895)
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	0	0	0	(45,698)
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, tax (expense) benefit	(855)	(922)	(2,574)	(2,755)
Other Comprehensive Income (Loss), Tax, Total	(3,283)	(14,895)	(16,650)	(60,348)
Other comprehensive income (loss), before reclassifications, net of tax amount	7,286	41,919	42,229	35,684
Reclassification from accumulated other comprehensive income, current period, net of tax amount	0	0	0	137,094
Other comprehensive income (loss), change in net unrealized holding loss on securities transferred to held to maturity, net of tax amount	2,567	2,766	7,723	8,265
Other comprehensive income (loss), net of tax amount	9,853	44,685	49,952	181,043
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	4	28	11	83
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(2)	(7)	(3)	(21)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	2	21	8	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	(29)	0	(79)	(13)
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	8	0	20	3
Reclassification from accumulated other comprehensive income, current period, net of tax amount	(21)	0	(59)	(10)
Change in Net Actuarial Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from accumulated other comprehensive income, current period, before tax amount	61	84	193	263
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(15)	(21)	(48)	(65)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	46	63	145	198
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	36	112	125	333
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(9)	(28)	(31)	(83)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	27	84	94	250
Cash Flow Hedge Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassifications, before tax amount	(822)	18,826	11,155	(2,007)
Reclassification from accumulated other comprehensive income, current period, before tax amount	2,462	4,831	7,823	14,520
Other comprehensive income (loss), before tax amount	1,640	23,657	18,978	12,513
Other comprehensive income (loss), before reclassifications, tax (expense) benefit	205	(4,706)	(2,789)	502
Reclassification from accumulated other comprehensive income, current period, tax (expense) benefit	(616)	(1,208)	(1,956)	(3,630)
Other Comprehensive Income (Loss), Tax, Total	(411)	(5,914)	(4,745)	(3,128)
Other comprehensive income (loss), before reclassifications, net of tax amount	(617)	14,120	8,366	(1,505)
Reclassification from accumulated other comprehensive income, current period, net of tax amount	1,846	3,623	5,867	10,890
Other comprehensive income (loss), net of tax amount	$ 1,229	$ 17,743	$ 14,233	$ 9,385