Estimated Fair Values (Estimated Fair Values For Certain Financial Assets And Financial Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 395,364	$ 362,048
Overnight investments	7,871,382	4,347,336
Debt Securities, Available-for-sale	7,381,083	7,014,243
Investment securities held to maturity at cost	3,394,604	2,816,982
Investment in marketable equity securities	118,540	91,680
Loans held for sale	107,800	124,800
Loans and Leases Receivable, Net Amount	32,500,558	32,567,661
Income earned not collected	133,043	145,694
Stock issued by Federal Home Loan Bank	40,500	45,400
Deposits	48,410,596	43,431,609
Securities sold under customer repurchase agreements	692,604	641,487
FDIC shared-loss payable	0	15,601
Subordinated Debt	497,290	504,518
Other Borrowings	80,531	88,470
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Federal Home Loan Bank Advances	646,667	655,175
Cash and due from banks	395,364	362,048
Overnight investments	7,871,382	4,347,336
Debt Securities, Available-for-sale	7,381,083	7,014,243
Investment securities held to maturity at cost	3,394,604	2,816,982
Investment in marketable equity securities	118,540	91,680
Loans held for sale	107,768	124,837
Loans and Leases Receivable, Net Amount	32,500,558	32,567,661
Income earned not collected	133,043	145,694
Stock issued by Federal Home Loan Bank	40,450	45,392
Mortgage servicing rights	22,702	19,628
Deposits	45,789,354	40,542,596
Time deposits	2,621,242	2,889,013
Securities sold under customer repurchase agreements	692,604	641,487
FDIC shared-loss payable	0	15,601
Accrued interest payable	8,811	9,414
Subordinated Debt	497,290	504,518
Other Borrowings	80,531	88,470
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Federal Home Loan Bank Advances	662,606	677,579
Cash and due from banks	395,364	362,048
Overnight investments	7,871,382	4,347,336
Debt Securities, Available-for-sale	7,381,083	7,014,243
Investment securities held to maturity at cost	3,377,085	2,838,499
Investment in marketable equity securities	118,540	91,680
Loans held for sale	107,768	124,837
Loans and Leases Receivable, Net Amount	32,786,935	33,298,166
Income earned not collected	133,043	145,694
Stock issued by Federal Home Loan Bank	40,450	45,392
Mortgage servicing rights	23,155	20,283
Deposits	45,789,354	40,542,596
Time deposits	2,626,322	2,905,577
Securities sold under customer repurchase agreements	692,604	641,487
FDIC shared-loss payable	0	15,843
Accrued interest payable	8,811	9,414
Subordinated Debt	523,423	525,610
Other Borrowings	$ 81,201	$ 89,263