Fair Value of Financial Instruments (Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	$ 2,910,869	$ 2,516,908
Held to maturity securities	2,977,511	2,500,220
Derivative financial instruments	2,148	4,788
Derivative financial instruments	3,938	26,846
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	479,332	450,866
Federal funds purchased	140,754	2,275
Securities sold under agreements to repurchase	430,569	358,131
Short-term FHLB Borrowings	1,132,567	865,000
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	2,910,869	2,516,908
Held to maturity securities	2,962,010	2,470,117
Loans, net	184,205	169,888
Loans held for sale	39,865	34,064
Derivative financial instruments	14,157	20,315
Long-term debt	303,631	435,747
Derivative financial instruments	14,389	27,432
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	18,403,303	16,326,961
Deposits	22,238,847	19,430,939
Total Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	479,332	450,866
Available for sale debt securities	2,910,869	2,516,908
Held to maturity securities	2,962,010	2,470,117
Loans, net	18,587,508	16,496,849
Loans held for sale	39,865	34,064
Derivative financial instruments	14,157	20,315
Deposits	22,238,847	19,430,939
Federal funds purchased	140,754	2,275
Securities sold under agreements to repurchase	430,569	358,131
Short-term FHLB Borrowings	1,132,567	865,000
Long-term debt	303,631	435,747
Derivative financial instruments	14,389	27,432
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	479,332	450,866
Available for sale debt securities	2,910,869	2,516,908
Held to maturity securities	2,977,511	2,500,220
Loans, net	18,786,855	16,522,733
Loans held for sale	39,865	34,064
Derivative financial instruments	14,157	20,315
Deposits	22,253,202	19,424,266
Federal funds purchased	140,754	2,275
Securities sold under agreements to repurchase	430,569	358,131
Short-term FHLB Borrowings	1,132,567	865,000
Long-term debt	305,513	436,280
Derivative financial instruments	$ 14,389	$ 27,432

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

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value portion of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

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Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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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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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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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. Includes loans held for sale. Excludes loans and leases covered under loss sharing agreements.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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