Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 160,577	$ 292,250
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Provision for credit losses	138,750	31,800
Deferred Income Tax Expense (Benefit)	(29,976)	3,647
Depreciation, Amortization and Accretion, Net	27,448	28,159
Accretion (Amortization) of Discounts and Premiums, Investments	47,178	36,667
Share-based Payment Arrangement, Noncash Expense	9,356	9,684
Gains (Losses) on Sales of Other Real Estate	(1,073)	(827)
Gain (Loss) on Disposition of Property Plant Equipment	184	1,213
Available-for-sale Securities, Gross Realized Gains	(8)	0
Life Insurance, Corporate or Bank Owned, Change in Value	(10,899)	(10,942)
Bank Owned Life Insurance Income	(352)	(4,626)
Gain (Loss) on Sales of Loans, Net	(14,185)	(3,829)
Proceeds from Sale of Loans Held-for-sale	342,747	129,700
Payments for Origination of Mortgage Loans Held-for-sale	(324,319)	(146,746)
Increase (Decrease) in Financial Instruments Used in Operating Activities	8,634	(4,274)
Increase (Decrease) in Derivative Assets and Liabilities	(172,647)	(164,977)
Increase (Decrease) in Other Operating Assets	23,353	(25,803)
Increase (Decrease) in Other Accounts Payable and Accrued Liabilities	(43,272)	(39,033)
Net Cash Provided by (Used in) Operating Activities, Total	161,496	132,063
Net Cash Provided by (Used in) Investing Activities [Abstract]
Payments to Acquire Debt Securities, Available-for-sale	(586,228)	(351,091)
Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale	422,572	394,369
Proceeds from Sale of Available-for-sale Securities	8,963	0
Payments to Acquire Held-to-maturity Securities	(1,005,535)	(1,289,977)
Proceeds from Maturities, Prepayments and Calls of Held-to-maturity Securities	655,521	400,779
Payments for (Proceeds from) Federal Home Loan Bank Stock	59,435	32,302
Payments for (Proceeds from) Other Investing Activities	(7,423)	(4,040)
Payments for (Proceeds from) Other Loans and Leases	(1,869,715)	(1,147,426)
Proceeds of Other Loans and Leases Held-for-investment	6,414	20,542
Proceeds from Life Insurance Policy	1,625	9,193
Proceeds from Sale of Foreclosed Assets	8,047	10,901
Proceeds from Sale of Productive Assets	641	0
Payments to Acquire Property, Plant, and Equipment	(14,016)	(18,771)
Net Cash Provided by (Used in) Investing Activities, Total	(2,319,699)	(1,943,219)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Increase (Decrease) in Deposits	3,590,551	1,421,819
Proceeds from FHLBank Borrowings, Financing Activities	3,775,000	5,725,000
Payments of FHLBank Borrowings, Financing Activities	(5,290,233)	(6,158,959)
Increase (Decrease) in Federal Funds Purchased and Securities Sold under Agreements to Repurchase, Net	261,391	628,818
Proceeds from Issuance of Senior Long-term Debt	0	300,000
Payments of Debt Issuance Costs	0	(3,642)
Payments of Ordinary Dividends, Common Stock	(108,882)	(103,971)
Payments of Ordinary Dividends, Preferred Stock and Preference Stock	(5,906)	(5,906)
Proceeds from Stock Options Exercised	118	621
Payments for Repurchase of Common Stock	(76,556)	(13,003)
Payments for Repurchase of Equity, Share-based Compensation	(3,375)	(6,289)
Net Cash Provided by (Used in) Financing Activities, Total	2,142,108	1,784,488
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect, Total	(16,095)	(26,668)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Beginning Balance	257,895	329,499
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Ending Balance	241,800	302,831
Supplemental Cash Flow Information [Abstract]
Interest Paid, Excluding Capitalized Interest, Operating Activities	103,550	151,859
Income Taxes Paid	77,376	90,574
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Real Estate Owned, Transfer to Real Estate Owned	5,178	7,224
Transfer of Portfolio Loans and Leases to Held-for-sale	5,805	15,968
Payments for Deposits	4,657	0
Lease Obligation Incurred	0	157,234
Liabilities Assumed	$ 0	$ 178,208