Fair Values Measurements and Fair Value of Financial Instruments (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Securities Available for Sale [Abstract]
Total Securities Available for Sale	$ 1,071,654,000us-gaap_AvailableForSaleSecurities	$ 1,013,171,000us-gaap_AvailableForSaleSecurities
Trading Securities	8,265,000us-gaap_TradingSecurities	7,793,000us-gaap_TradingSecurities
Liabilities [Abstract]
Collateral dependent impaired financing receivable with specific reserves	8,700,000
Allowance for loan and lease losses collateral dependent impaired loans with specific reserves	3,000,000
Liquidation expense ratio on impaired collateral minimum (in hundredths)	10.00%
Liquidation expense ratio on impaired collateral maximum (in hundredths)	35.00%
Financial assets [Abstract]
Securities held to maturity	461,224,000	454,994,000
Financial liabilities [Abstract]
Time deposits	996,437,000us-gaap_TimeDeposits	1,043,823,000us-gaap_TimeDeposits
Long-term debt	130,775,000us-gaap_LongTermDebt	130,945,000us-gaap_LongTermDebt
Junior subordinated debt	101,196,000	101,196,000
Significant Other Observable Inputs (Level 2) [Member] \| Carrying Amount [Member]
Financial assets [Abstract]
Securities held to maturity	456,773,000	454,361,000
Financial liabilities [Abstract]
Time deposits	996,437,000	1,043,823,000
Long-term debt	130,775,000	130,945,000
Junior subordinated debt	101,196,000	101,196,000
Significant Other Observable Inputs (Level 2) [Member] \| Estimated Fair Value [Member]
Financial assets [Abstract]
Securities held to maturity	461,224,000	454,994,000
Financial liabilities [Abstract]
Time deposits	993,633,000	1,038,877,000
Long-term debt	133,064,000	132,562,000
Junior subordinated debt	106,273,000	103,770,000
Significant Unobservable Inputs (Level 3) [Member] \| Carrying Amount [Member]
Financial assets [Abstract]
Net Loans	5,557,664,000	5,528,912,000
Significant Unobservable Inputs (Level 3) [Member] \| Estimated Fair Value [Member]
Financial assets [Abstract]
Net Loans	5,614,078,000	5,584,777,000
Recurring Basis [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	13,056,000	23,111,000
Federal Agency	402,751,000	329,914,000
State & municipal	38,423,000	37,570,000
Mortgage-backed	347,803,000	364,727,000
Collateralized mortgage obligations	254,074,000	242,129,000
Other securities	15,547,000	15,720,000
Total Securities Available for Sale	1,071,654,000	1,013,171,000
Trading Securities	8,265,000	7,793,000
Interest Rate Swaps	6,833,000	4,707,000
Total	1,086,752,000	1,025,671,000
Liabilities [Abstract]
Interest Rate Swaps	6,833,000	4,707,000
Total	6,833,000	4,707,000
Recurring Basis [Member] \| Quoted Prices in Active Market for Identical Assets (Level I) [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	13,056,000	23,111,000
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	7,641,000	7,612,000
Total Securities Available for Sale	20,697,000	30,723,000
Trading Securities	8,265,000	7,793,000
Interest Rate Swaps	0	0
Total	28,962,000	38,516,000
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]
U.S. Treasury	0	0
Federal Agency	402,751,000	329,914,000
State & municipal	38,423,000	37,570,000
Mortgage-backed	347,803,000	364,727,000
Collateralized mortgage obligations	254,074,000	242,129,000
Other securities	7,906,000	8,108,000
Total Securities Available for Sale	1,050,957,000	982,448,000
Trading Securities	0	0
Interest Rate Swaps	6,833,000	4,707,000
Total	1,057,790,000	987,155,000
Liabilities [Abstract]
Interest Rate Swaps	6,833,000	4,707,000
Total	6,833,000	4,707,000
Recurring Basis [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	0	0
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

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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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. This element may be used 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. Represents investments in bonds or similar securities issued by state, city, or local governments.

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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. Element may be used with the fair value disclosures required in the footnote disclosures to the financial statements, and used in the balance sheet and disclosure in the same submission. Represents other securities categorized as available-for-sale.

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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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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 Government Treasury 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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