Fair Value (Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	$ 2,414,680	$ 2,093,404
Held to maturity securities	2,428,432	2,370,388
Derivative financial instruments	1,352	224
Derivative financial instruments	36,267	21,034
Total Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	458,792	869,429
Available for sale securities	2,414,680	2,093,404
Held to maturity securities	2,482,540	2,375,851
Loans, net	16,052,714	15,427,803
Loans held for sale	42,545	20,434
Derivative financial instruments	36,554	23,251
Deposits	18,885,148	18,327,425
Federal funds purchased	1,250	10,100
Securities sold under agreements to repurchase	335,894	513,544
FHLB borrowings	738,812	900,000
Long-term debt	468,091	488,711
Derivative financial instruments	37,899	23,968
Total Fair Value [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	458,792	869,429
Available for sale securities	1,201	2,757
Federal funds purchased	1,250	10,100
Securities sold under agreements to repurchase	335,894	513,544
FHLB borrowings	738,812	900,000
Total Fair Value [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	2,413,479	2,090,647
Held to maturity securities	2,482,540	2,375,851
Loans, net	126,401	93,602
Loans held for sale	42,545	20,434
Derivative financial instruments	36,554	23,251
Long-term debt	468,091	488,711
Derivative financial instruments	37,899	23,968
Total Fair Value [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	15,926,313	15,334,201
Deposits	18,885,148	18,327,425
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	458,792	869,429
Available for sale securities	2,414,680	2,093,404
Held to maturity securities	2,428,432	2,370,388
Loans, net	15,834,760	15,522,135
Loans held for sale	42,545	20,434
Derivative financial instruments	36,554	23,251
Deposits	18,885,477	18,348,912
Federal funds purchased	1,250	10,100
Securities sold under agreements to repurchase	335,894	513,544
FHLB borrowings	738,812	900,000
Long-term debt	463,710	490,145
Derivative financial instruments	$ 37,899	$ 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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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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