Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 202,113	$ 91,296
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Provision for credit losses	(47,250)	116,000
Deferred Income Tax Expense (Benefit)	16,012	(27,020)
Depreciation, Amortization and Accretion, Net	18,683	18,110
Accretion (Amortization) of Discounts and Premiums, Investments	66,312	27,996
Share-based Payment Arrangement, Noncash Expense	6,433	6,014
Gains (Losses) on Sales of Other Real Estate	(141)	(664)
Gain (Loss) on Disposition of Property Plant Equipment	724	256
Available-for-sale Securities, Gross Realized Gains	0	(8)
Life Insurance, Corporate or Bank Owned, Change in Value	(7,136)	(7,204)
Bank Owned Life Insurance Income	(805)	(348)
Gain (Loss) on Sales of Loans, Net	(3,961)	(7,098)
Proceeds from Sale of Loans Held-for-sale	147,735	170,168
Payments for Origination of Mortgage Loans Held-for-sale	(135,930)	(175,228)
Increase (Decrease) in Financial Instruments Used in Operating Activities	1,336	3,395
Increase (Decrease) in Derivative Assets and Liabilities	106,759	(256,780)
Gain on sale of banking centers	(533)	0
Increase (Decrease) in Other Operating Assets	(91,177)	14,755
Increase (Decrease) in Other Accounts Payable and Accrued Liabilities	34,057	67,239
Net Cash Provided by (Used in) Operating Activities, Total	313,231	40,879
Net Cash Provided by (Used in) Investing Activities [Abstract]
Payments to Acquire Debt Securities, Available-for-sale	(504,286)	(479,330)
Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale	510,484	266,704
Proceeds from Sale of Available-for-sale Securities	0	8,963
Payments to Acquire Held-to-maturity Securities	(775,673)	(529,233)
Proceeds from Maturities, Prepayments and Calls of Held-to-maturity Securities	694,951	382,903
Payments for (Proceeds from) Federal Home Loan Bank Stock	720	54,551
Payments for (Proceeds from) Other Investing Activities	(5,568)	(1,103)
Payments for (Proceeds from) Other Loans and Leases	84,886	(1,797,719)
Proceeds of Other Loans and Leases Held-for-investment	49,122	3,606
Proceeds from Life Insurance Policy	2,683	1,019
Proceeds from Sale of Foreclosed Assets	523	4,667
Proceeds from Sale of Productive Assets	2,413	0
Payments to Acquire Property, Plant, and Equipment	(7,407)	(7,817)
Net Cash Provided by (Used in) Investing Activities, Total	52,848	(2,092,789)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Increase (Decrease) in Deposits	1,510,573	3,030,321
Proceeds from FHLBank Borrowings, Financing Activities	180,470	3,450,000
Payments of FHLBank Borrowings, Financing Activities	(175,190)	(4,875,155)
Increase (Decrease) in Federal Funds Purchased and Securities Sold under Agreements to Repurchase, Net	(488,231)	648,374
Payments of Ordinary Dividends, Common Stock	(72,349)	(72,806)
Payments of Ordinary Dividends, Preferred Stock and Preference Stock	(3,938)	(3,938)
Proceeds from Stock Options Exercised	3,386	118
Payments for Repurchase of Common Stock	0	(76,556)
Payments for Repurchase of Equity, Share-based Compensation	(4,011)	(3,219)
Net Cash Provided by (Used in) Financing Activities, Total	950,710	2,097,139
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect, Total	1,316,789	45,229
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Beginning Balance	263,104	257,895
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Ending Balance	1,579,893	303,124
Supplemental Cash Flow Information [Abstract]
Interest Paid, Excluding Capitalized Interest, Operating Activities	23,113	77,757
Income Taxes Paid	80,873	11,353
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Real Estate Owned, Transfer to Real Estate Owned	829	2,857
Transfer of Portfolio Loans and Leases to Held-for-sale	$ 48,395	$ 3,036