Accumulated Other Comprehensive Income (Loss) - Changes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pre-tax Amount
Other comprehensive loss, Pre-tax Amount	$ 148,713	$ (705,846)	$ (209,065)
Income Tax Benefit (Expense)
Other comprehensive loss, Income Tax Benefit (Expense)	(39,669)	188,285	55,768
Net of tax
Balance	2,269,005	2,656,912	2,744,104
Other comprehensive income (loss)	109,044	(517,561)	(153,297)
Balance	2,486,066	2,269,005	2,656,912
Accumulated other comprehensive loss
Pre-tax Amount
Accumulated other comprehensive loss, beginning balance, Pre-tax Amount	(871,813)	(165,967)	43,098
Accumulated other comprehensive loss, ending balance, Pre-tax Amount	(723,100)	(871,813)	(165,967)
Income Tax Benefit (Expense)
Accumulated other comprehensive loss, beginning balance, Income Tax Benefit (Expense)	232,559	44,274	(11,494)
Accumulated other comprehensive loss, ending balance, Income Tax Benefit (Expense)	192,890	232,559	44,274
Net of tax
Balance	(639,254)	(121,693)	31,604
Other comprehensive income (loss)	109,044	(517,561)	(153,297)
Balance	(530,210)	(639,254)	(121,693)
Pensions and Other Benefits
Pre-tax Amount
Unrealized net losses arising during the period, Pre-tax Amount	79	25,856	10,020
Income Tax Benefit (Expense)
Unrealized net losses arising during the period, Income Tax Benefit (Expense)	(21)	(6,897)	(2,673)
Net of tax
Balance	(5,431)	(24,390)	(31,737)
Unrealized net losses arising during the period, Net of tax	58	18,959	7,347
Other comprehensive income (loss)	58	18,959	7,347
Balance	(5,373)	(5,431)	(24,390)
Pension and other benefits, net actuarial losses arising during the year
Pre-tax Amount
Unrealized net losses arising during the period, Pre-tax Amount	(1,063)	20,710	3,107
Income Tax Benefit (Expense)
Unrealized net losses arising during the period, Income Tax Benefit (Expense)	284	(5,524)	(829)
Net of tax
Unrealized net losses arising during the period, Net of tax	(779)	15,186	2,278
Pension and other benefits: Amortization of net loss included in net income
Pre-tax Amount
Unrealized net losses arising during the period, Pre-tax Amount	1,142	5,146	6,913
Income Tax Benefit (Expense)
Unrealized net losses arising during the period, Income Tax Benefit (Expense)	(305)	(1,373)	(1,844)
Net of tax
Unrealized net losses arising during the period, Net of tax	837	3,773	5,069
Investment securities
Pre-tax Amount
Unrealized net losses arising during the period, Pre-tax Amount	55,141	(773,667)	(218,983)
Reclassification of net losses (gains) to net income, Pre-tax Amount	39,986	48,378
Other comprehensive loss, Pre-tax Amount	143,317	(725,289)
Income Tax Benefit (Expense)
Unrealized net losses arising during the period, Income Tax Benefit (Expense)	(14,709)	206,376	58,414
Reclassification of net (losses) gains to net income, Income Tax Benefit (Expense)	(10,666)	(12,905)
Other comprehensive loss, Income Tax Benefit (Expense)	(38,230)	193,471
Net of tax
Unrealized net losses arising during the period, Net of tax	40,432	(567,291)	(160,569)
Reclassification of net gains (losses) to net income, Net of tax	29,320	35,473
Other comprehensive income (loss)	105,087	(531,818)
Amortization of unrealized holding losses on held-to-maturity securities
Pre-tax Amount
Reclassification of net losses (gains) to net income, Pre-tax Amount	48,190
Income Tax Benefit (Expense)
Reclassification of net (losses) gains to net income, Income Tax Benefit (Expense)	12,855
Net of tax
Reclassification of net gains (losses) to net income, Net of tax	35,335
Cash Flow Derivative Hedges.
Pre-tax Amount
Unrealized net losses arising during the period, Pre-tax Amount	(940)	(6,710)
Reclassification of net losses (gains) to net income, Pre-tax Amount	6,257	297
Other comprehensive loss, Pre-tax Amount	5,317	(6,413)
Income Tax Benefit (Expense)
Unrealized net losses arising during the period, Income Tax Benefit (Expense)	251	1,790
Reclassification of net (losses) gains to net income, Income Tax Benefit (Expense)	1,669	(79)
Other comprehensive loss, Income Tax Benefit (Expense)	(1,418)	1,711
Net of tax
Balance	(4,702)
Unrealized net losses arising during the period, Net of tax	(689)	(4,920)
Reclassification of net gains (losses) to net income, Net of tax	4,588	218
Other comprehensive income (loss)	3,899	(4,702)
Balance	(803)	(4,702)
Available-for-sale Investment securities
Pre-tax Amount
Unrealized net losses arising during the period, Pre-tax Amount			(219,085)
Reclassification of net losses (gains) to net income, Pre-tax Amount			(102)
Income Tax Benefit (Expense)
Unrealized net losses arising during the period, Income Tax Benefit (Expense)			58,441
Reclassification of net (losses) gains to net income, Income Tax Benefit (Expense)			27
Net of tax
Balance	(292,175)	(97,303)	63,341
Unrealized net losses arising during the period, Net of tax			(160,644)
Reclassification of net gains (losses) to net income, Net of tax			(75)
Other comprehensive income (loss)	69,752	(567,291)	(160,644)
Balance	$ (222,423)	$ (292,175)	$ (97,303)