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Fair Value Measurements Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure $ 2,259,802us-gaap_AvailableForSaleSecurities $ 2,323,371us-gaap_AvailableForSaleSecurities
Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Mortgages Held-for-sale, Fair Value Disclosure 34,124us-gaap_MortgagesHeldForSaleFairValueDisclosure
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17,522us-gaap_MortgagesHeldForSaleFairValueDisclosure
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Available-for-sale Securities, Fair Value Disclosure 2,259,802us-gaap_AvailableForSaleSecurities
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2,323,371us-gaap_AvailableForSaleSecurities
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Other Assets, Fair Value Disclosure 50,855us-gaap_OtherAssetsFairValueDisclosure
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38,987us-gaap_OtherAssetsFairValueDisclosure
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Assets, Fair Value Disclosure 2,344,781us-gaap_AssetsFairValueDisclosure
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2,379,880us-gaap_AssetsFairValueDisclosure
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Liabilities, Fair Value Disclosure 48,769us-gaap_LiabilitiesFairValueDisclosure
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38,821us-gaap_LiabilitiesFairValueDisclosure
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Equity Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 40,608us-gaap_AvailableForSaleSecurities
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47,623us-gaap_AvailableForSaleSecurities
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Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 40,608us-gaap_AvailableForSaleSecurities
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47,623us-gaap_AvailableForSaleSecurities
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U.S. Government Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure   200us-gaap_AvailableForSaleSecurities
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U.S. Government Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure   200us-gaap_AvailableForSaleSecurities
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U.S. Government-Sponsored Agency Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 203us-gaap_AvailableForSaleSecurities
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214us-gaap_AvailableForSaleSecurities
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U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 203us-gaap_AvailableForSaleSecurities
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State and Municipal Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 224,342us-gaap_AvailableForSaleSecurities
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245,215us-gaap_AvailableForSaleSecurities
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State and Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 224,342us-gaap_AvailableForSaleSecurities
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245,215us-gaap_AvailableForSaleSecurities
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Corporate Debt Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 97,682us-gaap_AvailableForSaleSecurities
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98,034us-gaap_AvailableForSaleSecurities
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Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 97,682us-gaap_AvailableForSaleSecurities
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98,034us-gaap_AvailableForSaleSecurities
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Collateralized Mortgage Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 867,876us-gaap_AvailableForSaleSecurities
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902,313us-gaap_AvailableForSaleSecurities
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Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 867,876us-gaap_AvailableForSaleSecurities
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902,313us-gaap_AvailableForSaleSecurities
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Mortgage-Backed Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 930,159us-gaap_AvailableForSaleSecurities
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928,831us-gaap_AvailableForSaleSecurities
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Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 930,159us-gaap_AvailableForSaleSecurities
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928,831us-gaap_AvailableForSaleSecurities
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Auction Rate Securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 98,932us-gaap_AvailableForSaleSecurities
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100,941us-gaap_AvailableForSaleSecurities
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Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 98,932us-gaap_AvailableForSaleSecurities
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100,941us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Mortgages Held-for-sale, Fair Value Disclosure 0us-gaap_MortgagesHeldForSaleFairValueDisclosure
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Available-for-sale Securities, Fair Value Disclosure 40,608us-gaap_AvailableForSaleSecurities
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47,623us-gaap_AvailableForSaleSecurities
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Other Assets, Fair Value Disclosure 19,198us-gaap_OtherAssetsFairValueDisclosure
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17,682us-gaap_OtherAssetsFairValueDisclosure
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Assets, Fair Value Disclosure 59,806us-gaap_AssetsFairValueDisclosure
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65,305us-gaap_AssetsFairValueDisclosure
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Liabilities, Fair Value Disclosure 19,009us-gaap_LiabilitiesFairValueDisclosure
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17,737us-gaap_LiabilitiesFairValueDisclosure
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Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 40,608us-gaap_AvailableForSaleSecurities
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47,623us-gaap_AvailableForSaleSecurities
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure   0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 1 [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 1 [Member] | State and Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
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Fair Value, Inputs, Level 2 [Member] | U.S. Government Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure   200us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 2 [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
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Fair Value, Inputs, Level 2 [Member] | State and Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 224,342us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
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Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
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Fair Value, Inputs, Level 2 [Member] | Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
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Fair Value, Inputs, Level 2 [Member] | Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Mortgages Held-for-sale, Fair Value Disclosure 0us-gaap_MortgagesHeldForSaleFairValueDisclosure
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Other Assets, Fair Value Disclosure 0us-gaap_OtherAssetsFairValueDisclosure
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Liabilities, Fair Value Disclosure 0us-gaap_LiabilitiesFairValueDisclosure
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Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 3 [Member] | U.S. Government Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure   0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 3 [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 3 [Member] | State and Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 4,904us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 3 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 3 [Member] | Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure 0us-gaap_AvailableForSaleSecurities
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Fair Value, Inputs, Level 3 [Member] | Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available-for-sale Securities, Fair Value Disclosure $ 98,932us-gaap_AvailableForSaleSecurities
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