Fair Value of Financial Instruments (Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	$ 2,516,908	$ 2,093,404
Held to maturity securities	2,500,220	2,370,388
Derivative financial instruments	4,788	224
Derivative financial instruments	26,846	21,034
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	450,866	869,429
Available for sale securities		2,757
Federal funds purchased	2,275	10,100
Securities sold under agreements to repurchase	358,131	513,544
FHLB borrowings	865,000	900,000
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	2,516,908	2,090,647
Held to maturity securities	2,470,117	2,375,851
Loans, net	169,888	93,602
Loans held for sale	34,064	20,434
Derivative financial instruments	20,315	23,251
Long-term debt	435,747	494,565
Derivative financial instruments	27,432	23,968
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	16,326,961	15,334,201
Deposits	19,430,939	18,327,425
Total Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	450,866	869,429
Available for sale securities	2,516,908	2,093,404
Held to maturity securities	2,470,117	2,375,851
Loans, net	16,496,849	15,427,803
Loans held for sale	34,064	20,434
Derivative financial instruments	20,315	23,251
Deposits	19,430,939	18,327,425
Federal funds purchased	2,275	10,100
Securities sold under agreements to repurchase	358,131	513,544
FHLB borrowings	865,000	900,000
Long-term debt	435,747	494,565
Derivative financial instruments	27,432	23,968
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	450,866	869,429
Available for sale securities	2,516,908	2,093,404
Held to maturity securities	2,500,220	2,370,388
Loans, net	16,522,733	15,522,135
Loans held for sale	34,064	20,434
Derivative financial instruments	20,315	23,251
Deposits	19,424,266	18,348,912
Federal funds purchased	2,275	10,100
Securities sold under agreements to repurchase	358,131	513,544
FHLB borrowings	865,000	900,000
Long-term debt	436,280	495,999
Derivative financial instruments	$ 27,432	$ 23,968

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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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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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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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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