Estimated Fair Values (Estimated Fair Values For Certain Financial Assets And Financial Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 502,273	$ 539,741
Overnight investments	2,736,514	1,872,594
Investment securities available for sale	7,119,861	7,006,580
Investment securities held to maturity	83	98
Loans held for sale	49,952	74,401
Loans and Leases Receivable, Net Amount	21,685,506	21,519,083
FDIC shared-loss receivable	3,981	4,172	$ 7,474	$ 4,054
Income earned not collected	80,456	79,839
Mortgage servicing rights	20,771	20,415	$ 17,186	$ 19,351
Deposits	29,002,768	28,161,343
FDIC shared-loss payable	98,013	97,008
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	502,273	539,741
Overnight investments	2,736,514	1,872,594
Investment securities available for sale	7,119,861	7,006,580
Investment securities held to maturity	83	98
Loans held for sale	49,952	74,401
Loans and Leases Receivable, Net Amount	21,685,506	21,519,083
FDIC shared-loss receivable	3,981	4,172
Income earned not collected	80,456	79,839
Stock issued by Federal Home Loan Bank	43,495	43,495
Mortgage servicing rights	20,771	20,415
Deposits	29,002,768	28,161,343
Short-term borrowings	795,587	603,487
Long-term obligations	727,500	832,942
FDIC shared-loss payable	98,013	97,008
Accrued interest payable	3,947	3,797
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	502,273	539,741
Overnight investments	2,736,514	1,872,594
Investment securities available for sale	7,119,861	7,006,580
Investment securities held to maturity	89	104
Loans held for sale	49,952	74,401
Loans and Leases Receivable, Net Amount	20,727,792	20,614,548
FDIC shared-loss receivable	3,981	4,172
Income earned not collected	80,456	79,839
Stock issued by Federal Home Loan Bank	43,495	43,495
Mortgage servicing rights	25,690	24,446
Deposits	28,976,211	28,135,698
Short-term borrowings	795,587	603,487
Long-term obligations	713,402	832,201
FDIC shared-loss payable	100,948	100,069
Accrued interest payable	$ 3,947	$ 3,797