Estimated Fair Values (Estimated Fair Values For Certain Financial Assets And Financial Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 268,599	$ 327,440
Overnight investments	1,386,525	797,406
Investment securities held to maturity	2,214,829	2,184,653
Investment in marketable equity securities	109,884	92,599
Loans held for sale	53,232	45,505
Loans and Leases Receivable, Net Amount	25,235,010	25,299,564
Income earned not collected	113,812	109,903
Mortgage servicing rights	20,647	21,396	$ 21,659	$ 21,945
Deposits	31,198,093	30,672,460
Securities sold under customer repurchase agreements	508,508	543,936
Federal Home Loan Bank borrowings	189,594	193,556
FDIC shared-loss payable	107,256	105,618
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	268,599	327,440
Overnight investments	1,386,525	797,406
Debt Securities, Available-for-sale	4,589,800	4,557,110
Investment securities held to maturity	2,214,829	2,184,653
Investment in marketable equity securities	109,884	92,599
Loans held for sale	53,232	45,505
Loans and Leases Receivable, Net Amount	25,235,010	25,299,564
Income earned not collected	113,812	109,903
Stock issued by Federal Home Loan Bank	25,174	25,304
Mortgage servicing rights	24,080	24,615
Deposits	31,198,093	30,672,460
Securities sold under customer repurchase agreements	508,508	543,936
Federal Home Loan Bank borrowings	189,594	193,556
Short-term borrowings	136,544	140,741
Long-term obligations	14,970	13,921
FDIC shared-loss payable	107,256	105,618
Accrued interest payable	7,169	3,712
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	268,599	327,440
Overnight investments	1,386,525	797,406
Debt Securities, Available-for-sale	4,589,800	4,557,110
Investment securities held to maturity	2,254,924	2,201,502
Investment in marketable equity securities	109,884	92,599
Loans held for sale	53,232	45,505
Loans and Leases Receivable, Net Amount	25,187,938	24,845,060
Income earned not collected	113,812	109,903
Stock issued by Federal Home Loan Bank	25,174	25,304
Mortgage servicing rights	25,769	27,435
Deposits	31,174,142	30,623,214
Securities sold under customer repurchase agreements	508,508	543,936
Federal Home Loan Bank borrowings	192,779	195,374
Short-term borrowings	140,676	151,670
Long-term obligations	14,833	13,985
FDIC shared-loss payable	109,947	105,846
Accrued interest payable	$ 7,169	$ 3,712

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 security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

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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 of investment in debt security measured at amortized cost (held-to-maturity).

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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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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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