Estimated Fair Values (Estimated Fair Values For Certain Financial Assets And Financial Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 248,139	$ 336,150
Overnight investments	1,946,882	1,387,927
Investment securities available for sale	6,857,740	7,180,180
Investment securities held to maturity	74	76
Marketable equity securities	110,107	0
Loans held for sale	46,660	51,179
Loans and Leases Receivable, Net Amount	23,388,861	23,374,932
FDIC shared-loss receivable	3,636	2,223	$ 3,981	$ 4,172
Income earned not collected	96,607	95,249
Mortgage servicing rights	21,659	21,945	20,771	20,415
Deposits	29,969,245	29,266,275
FDIC shared-loss payable	102,466	101,342	$ 98,013	$ 97,008
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	248,139	336,150
Overnight investments	1,946,882	1,387,927
Investment securities available for sale	6,857,740	7,180,180
Investment securities held to maturity	74	76
Marketable equity securities	110,107	0
Loans held for sale	46,660	51,179
Loans and Leases Receivable, Net Amount	23,388,861	23,374,932
FDIC shared-loss receivable	3,636	2,223
Income earned not collected	96,607	95,249
Stock issued by Federal Home Loan Bank	20,810	52,685
Mortgage servicing rights	21,659	21,945
Deposits	29,969,245	29,266,275
Short-term borrowings	554,758	693,807
Long-term obligations	194,413	870,240
FDIC shared-loss payable	102,466	101,342
Accrued interest payable	1,498	3,952
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	248,139	336,150
Overnight investments	1,946,882	1,387,927
Investment securities available for sale	6,857,740	7,180,180
Investment securities held to maturity	79	81
Marketable equity securities	110,107	0
Loans held for sale	46,660	51,179
Loans and Leases Receivable, Net Amount	22,672,287	22,257,803
FDIC shared-loss receivable	3,636	2,223
Income earned not collected	96,607	95,249
Stock issued by Federal Home Loan Bank	20,810	52,685
Mortgage servicing rights	27,512	26,170
Deposits	29,924,950	29,230,768
Short-term borrowings	554,758	693,807
Long-term obligations	203,061	852,112
FDIC shared-loss payable	103,440	102,684
Accrued interest payable	$ 1,498	$ 3,952

Payable to FDIC for Loss Share Agreements

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For an unclassified balance sheet, the amount of fees and other revenue, excluding investment income receivable, earned but not yet received, which were recognized in conformity with revenue recognition criteria based on estimates or specific contractual terms.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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For banks and other depository institutions: Includes cash on hand (currency and coin), cash items in process of collection, noninterest bearing deposits due from other financial institutions (including corporate credit unions), and noninterest bearing balances with the Federal Reserve Banks, Federal Home Loan Banks and central banks.

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Carrying amount of receivable assets originating from the indemnification agreement with the Federal Deposit Insurance Corporation (FDIC), in which the FDIC is to partially cover losses.

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Amount of interest payable on debt, including, but not limited to, trade payables.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of short-term investments classified as other.

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Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

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