Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract]
Net Income (Loss)	$ 123,564	$ 119,635	$ 111,230	$ 101,687	$ 243,200	$ 212,916
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract]
Provision for Loan, Lease, and Other Losses	19,388		17,996		30,389	30,999
Depreciation					24,824	26,006
Mortgage Servicing Rights (MSR) Impairment (Recovery)					(86)	1,632
Amortization of Intangible Assets	6,894		2,203		9,096	4,405
Accretion (Amortization) of Discounts and Premiums, Investments					15,062	18,278
Other Depreciation and Amortization					17,146	17,058
Marketable Securities, Gain (Loss)					4	0
Gain (Loss) on Disposition of Assets	(789)		1,735		(1,629)	2,613
(Gain) loss on mortgage banking activities, net					911	(683)
Gain (Loss) on Sale of Mortgage Loans	0		0		0	6,976
Increase (Decrease) in Obligation, Pension Benefits					(12,308)	(12,372)
Payment for Origination and Purchase, Loan, Held-for-Sale					(367,223)	(273,947)
Proceeds from Sale, Loan, Mortgage, Held-for-Sale					352,641	238,557
Increase (Decrease) in Other Operating Assets and Liabilities, Net [Abstract]
Increase (Decrease) in Accrued Interest Receivable, Net					(898)	(854)
Decrease in net income tax position					34,744	49,335
Increase (Decrease) in Interest Payable, Net					1,610	(3,681)
Increase (Decrease) in Other Accounts Payable and Accrued Liabilities					(53,437)	(11,116)
Increase (Decrease) in Derivative Assets and Liabilities					16,624	(50,962)
Increase (Decrease) in Other Noncurrent Assets					(8,430)	(9,339)
Increase (Decrease) in Other Operating Assets and Liabilities, Net					40,720	(6,184)
Net Cash Provided by (Used in) Operating Activities, Total					342,960	239,637
Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract]
Payments for (Proceeds from) Loans and Leases					(1,593,324)	(865,086)
Payment for Investing Activity [Abstract]
Payments to Acquire Debt Securities, Available-for-Sale					(1,815,271)	(910,262)
Payments to Acquire Held-to-Maturity Securities					0	(994)
Payments to Acquire Federal Home Loan Bank Stock					(130,630)	(177,712)
Proceeds from Investing Activity [Abstract]
Proceeds from Sale of Debt Securities, Available-for-Sale					995,830	0
Proceeds from Sale of Held-to-Maturity Securities					1,221	0
Proceeds from Sale of Federal Home Loan Bank Stock					53,765	76,535
Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-Sale					772,971	504,380
Proceeds from Maturities, Prepayments and Calls of Held-to-Maturity Securities					92,018	69,279
Proceeds from Sale and Maturity of Other Investments					9,756	7,813
Proceeds from Sale of Mortgage Portfolio					0	564,375
Payments for (Proceeds from) Productive Assets					(21,046)	(18,046)
Net Change in Tax Credit Investments					(12,499)	(14,903)
Net cash received from the American National acquisition					220,898	0
Net Cash Provided by (Used in) Investing Activities, Total					(1,426,311)	(764,621)
Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract]
Increase (Decrease) in Deposits					(166,364)	(500,869)
Proceeds from (Repayments of) Short-Term Debt					207,090	(394,784)
Increase (Decrease) in Loans from Federal Home Loan Banks					1,417,750	2,220,000
Payments of FHLBank Borrowings, Financing Activities					(151,007)	(400,065)
Proceeds from FHLBank Borrowings, Financing Activities					0	200,000
Finance Lease, Principal Payments					0	(45)
Repayments of Senior Debt					0	(250,000)
Proceeds, Issuance of Shares, Share-Based Payment Arrangement, Including Option Exercised					10,233	2,286
Payments of Ordinary Dividends, Common Stock					(85,799)	(77,036)
Payments of Ordinary Dividends, Preferred Stock and Preference Stock					(5,750)	(5,750)
Proceeds from (Payment for) Other Financing Activity					0	(52)
Net Cash Provided by (Used in) Financing Activities, Total					1,193,921	765,485
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect, Total					110,570	240,501
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Beginning Balance		1,720,221		1,019,604	1,720,221	1,019,604	$ 1,019,604
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Ending Balance	1,830,791		1,260,105		1,830,791	1,260,105	1,720,221
Supplemental Cash Flow Information [Abstract]
Interest Paid, Excluding Capitalized Interest, Operating Activity					469,929	488,277
Stock Issued					594,144	0
Fair Value of Assets Acquired					5,228,544	0
Liabilities Assumed					4,634,400	0
Servicing Asset at Fair Value, Additions					6,159		$ 8,716
Board Authorized Purchase Program [Member]
Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract]
Payments for Repurchase of Common Stock					(25,202)	(22,292)
Performance/Service Based RSAs, RSA,
Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract]
Payments for Repurchase of Common Stock					(7,030)	(5,910)
Retained Earnings [Member]
Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract]
Net Income (Loss)	$ 123,564	$ 119,635	$ 111,230	$ 101,687	$ 243,200	$ 212,916