Fair Value Measurements and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Securities Available for Sale [Abstract]
Total Securities Available for Sale	$ 1,259,874	$ 1,174,544
Trading Securities	8,905	8,377
Liabilities [Abstract]
Allowance for loan and lease losses collateral dependent impaired loans with specific reserves	$ 3,000		$ 3,000
Liquidation expense ratio on impaired collateral minimum	10.00%
Liquidation expense ratio on impaired collateral maximum	35.00%
Financial assets [Abstract]
Securities held to maturity	$ 475,110	473,140
Financial liabilities [Abstract]
Time deposits	888,658	908,827
Long-term debt	130,377	130,447
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Securities held to maturity	466,914	471,031
Financial liabilities [Abstract]
Time deposits	888,658	908,827
Long-term debt	130,377	130,447
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Net Loans	5,903,491	5,820,115
Estimated Fair Value [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Securities held to maturity	475,110	473,140
Financial liabilities [Abstract]
Time deposits	889,278	903,501
Long-term debt	132,137	131,268
Junior subordinated debt	92,011	97,346
Estimated Fair Value [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Net Loans	6,062,550	5,958,427
Recurring Basis [Member]
Securities Available for Sale [Abstract]
Federal Agency	276,302	311,272
State & municipal	40,376	31,637
Mortgage-backed	417,800	409,896
Collateralized mortgage obligations	505,675	404,971
Other securities	19,721	16,768
Total Securities Available for Sale	1,259,874	1,174,544
Trading Securities	8,905	8,377
Interest Rate Swaps	12,121	6,224
Total	1,280,900	1,189,145
Liabilities [Abstract]
Interest Rate Swaps	12,121	6,224
Total	12,121	6,224
Recurring Basis [Member] \| Quoted Prices in Active Market for Identical Assets (Level I) [Member]
Securities Available for Sale [Abstract]
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	10,381	7,526
Total Securities Available for Sale	10,381	7,526
Trading Securities	8,905	8,377
Interest Rate Swaps	0	0
Total	19,286	15,903
Liabilities [Abstract]
Interest Rate Swaps	0	0
Total	0	0
Recurring Basis [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Securities Available for Sale [Abstract]
Federal Agency	276,302	311,272
State & municipal	40,376	31,637
Mortgage-backed	417,800	409,896
Collateralized mortgage obligations	505,675	404,971
Other securities	9,340	9,242
Total Securities Available for Sale	1,249,493	1,167,018
Trading Securities	0	0
Interest Rate Swaps	12,121	6,224
Total	1,261,614	1,173,242
Liabilities [Abstract]
Interest Rate Swaps	12,121	6,224
Total	12,121	6,224
Recurring Basis [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Securities Available for Sale [Abstract]
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	0	0
Total Securities Available for Sale	0	0
Trading Securities	0	0
Interest Rate Swaps	0	0
Total	0	0
Liabilities [Abstract]
Interest Rate Swaps	0	0
Total	0	$ 0
Nonrecurring Basis [Member]
Liabilities [Abstract]
Collateral dependent impaired financing receivable with specific reserves	$ 9,000		$ 8,700

Collateral dependent impaired loans with specific reserves included in the allowance for loan losses.

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Collateral dependent impaired loans which had specific reserves.

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Represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. May be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. May be used in both the balance sheet and disclosure in the same submission. Represents collateralized mortgage obligations as of the balance sheet date which have been categorized as available-for-sale.

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The maximum percentage of liquidation expenses estimated with liquidating impaired collateral.

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The minimum percentage of liquidation expenses estimated with liquidating impaired collateral.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity 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. This item represents investments in US Agency securities.

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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

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Fair value of investments in debt securities classified as held-to-maturity.

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

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Fair value of financial and nonfinancial obligations.

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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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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as available-for-sale.

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Amount of deposits that cannot be withdrawn before a set date without penalty or for which notice of withdrawal is required. Time deposits include, but are not limited to, certificates of deposits, individual retirement accounts and open accounts.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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