Fair Value (Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	$ 2,794,382	$ 2,516,908
Held to maturity securities	2,874,454	2,500,220
Derivative financial instruments	1,345	4,788
Derivative financial instruments	5,763	26,846
Total Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	491,653	450,866
Available for sale debt securities	2,794,382	2,516,908
Held to maturity securities	2,866,529	2,470,117
Loans, net	18,092,405	16,496,849
Loans held for sale	26,787	34,064
Derivative financial instruments	16,875	20,315
Deposits	21,432,877	19,430,939
Federal funds purchased	76,798	2,275
Securities sold under agreements to repurchase	482,109	358,131
FHLB short-term borrowings	1,252,000	865,000
Long-term debt	407,409	435,747
Derivative financial instruments	12,213	27,432
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	491,653	450,866
Federal funds purchased	76,798	2,275
Securities sold under agreements to repurchase	482,109	358,131
FHLB short-term borrowings	1,252,000	865,000
Total Fair Value [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	2,794,382	2,516,908
Held to maturity securities	2,866,529	2,470,117
Loans, net	137,653	169,888
Loans held for sale	26,787	34,064
Derivative financial instruments	16,875	20,315
Long-term debt	407,409	435,747
Derivative financial instruments	12,213	27,432
Total Fair Value [Member] \| Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	17,954,752	16,326,961
Deposits	21,432,877	19,430,939
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold	491,653	450,866
Available for sale debt securities	2,794,382	2,516,908
Held to maturity securities	2,874,454	2,500,220
Loans, net	18,251,976	16,522,733
Loans held for sale	26,787	34,064
Derivative financial instruments	16,875	20,315
Deposits	21,442,815	19,424,266
Federal funds purchased	76,798	2,275
Securities sold under agreements to repurchase	482,109	358,131
FHLB short-term borrowings	1,252,000	865,000
Long-term debt	407,876	436,280
Derivative financial instruments	$ 12,213	$ 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 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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