Condensed Consolidated Statements of Cash Flows (Unaudited) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 91,296	$ 198,385
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Provision for credit losses	116,000	20,500
Deferred Income Tax Expense (Benefit)	(27,020)	514
Depreciation, Amortization and Accretion, Net	18,110	18,884
Accretion (Amortization) of Discounts and Premiums, Investments	27,996	22,785
Share-based Payment Arrangement, Noncash Expense	6,014	6,416
Gains (Losses) on Sales of Other Real Estate	(664)	(635)
Gain (Loss) on Disposition of Property Plant Equipment	256	482
Available-for-sale Securities, Gross Realized Gains	(8)	0
Life Insurance, Corporate or Bank Owned, Change in Value	(7,204)	(7,234)
Bank Owned Life Insurance Income	(348)	(3,412)
Gain (Loss) on Sales of Loans, Net	(7,098)	(1,696)
Proceeds from Sale of Loans Held-for-sale	170,168	63,464
Payments for Origination of Mortgage Loans Held-for-sale	(175,228)	(74,076)
Increase (Decrease) in Financial Instruments Used in Operating Activities	3,395	(888)
Increase (Decrease) in Derivative Assets and Liabilities	(256,780)	(115,498)
Increase (Decrease) in Other Operating Assets	14,755	(28,485)
Increase (Decrease) in Other Accounts Payable and Accrued Liabilities	67,239	(1,545)
Net Cash Provided by (Used in) Operating Activities, Total	40,879	97,961
Net Cash Provided by (Used in) Investing Activities [Abstract]
Payments to Acquire Debt Securities, Available-for-sale	(479,330)	(255,885)
Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale	266,704	251,957
Proceeds from Sale of Available-for-sale Securities	8,963	0
Payments to Acquire Held-to-maturity Securities	(529,233)	(567,118)
Proceeds from Maturities, Prepayments and Calls of Held-to-maturity Securities	382,903	242,511
Payments for (Proceeds from) Federal Home Loan Bank Stock	54,551	30,915
Payments for (Proceeds from) Other Investing Activities	(1,103)	(3,316)
Payments for (Proceeds from) Other Loans and Leases	(1,797,719)	(847,143)
Proceeds of Other Loans and Leases Held-for-investment	3,606	20,012
Proceeds from Life Insurance Policy	1,019	2,270
Proceeds from Sale of Foreclosed Assets	4,667	8,191
Payments to Acquire Property, Plant, and Equipment	(7,817)	(12,698)
Net Cash Provided by (Used in) Investing Activities, Total	(2,092,789)	(1,130,304)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Increase (Decrease) in Deposits	3,030,321	738,802
Proceeds from FHLBank Borrowings, Financing Activities	3,450,000	3,700,000
Payments of FHLBank Borrowings, Financing Activities	(4,875,155)	(4,100,152)
Increase (Decrease) in Federal Funds Purchased and Securities Sold under Agreements to Repurchase, Net	648,374	375,046
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	(72,806)	(67,165)
Payments of Ordinary Dividends, Preferred Stock and Preference Stock	(3,938)	(3,938)
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	(3,219)	(6,245)
Net Cash Provided by (Used in) Financing Activities, Total	2,097,139	920,324
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect, Total	45,229	(112,019)
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	303,124	217,480
Supplemental Cash Flow Information [Abstract]
Interest Paid, Excluding Capitalized Interest, Operating Activities	77,757	87,129
Income Taxes Paid	11,353	69,759
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Real Estate Owned, Transfer to Real Estate Owned	2,857	5,880
Transfer of Portfolio Loans and Leases to Held-for-sale	3,036	15,438
Operating Lease, Right-of-Use Asset	151,805
Less: Present value adjustment	170,731
Liabilities Assumed	0	178,208
Lease Obligation Incurred	$ 0	$ 157,234