Investment Securities - Amortized Cost and Estimated Fair Value of Investments in Debt Securities by Contractual Maturity (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Estimated Fair Value	$ 1,301,915us-gaap_AvailableForSaleSecurities	$ 1,176,266us-gaap_AvailableForSaleSecurities
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
U.S. Government sponsored entities’ asset-backed securities	140,562us-gaap_HeldToMaturitySecurities	182,061us-gaap_HeldToMaturitySecurities
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
U.S. Government sponsored entities’ asset-backed securities	143,490	187,402
Obligations of U.S. Treasury and other U.S. Government sponsored entities
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Due one through five years	30,000
Due five through ten years	516,886
Total	546,886
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Due one through five years	30,011
Due five through ten years	508,053
Estimated Fair Value	538,064	525,136
Available for Sale Securities Weighted Avg Yield	2.34%
Available for Sale Securities Debt Maturities After Five Through Ten Years Weighted Avg Yield	2.35%
Available for Sale Securities Debt Maturities After One Through Five Years Weighted Avg Yield	2.10%
Obligations of States and Political Subdivisions
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
U.S. Government sponsored entities’ asset-backed securities		240
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
U.S. Government sponsored entities’ asset-backed securities		241
U.S. Government sponsored entity asset-backed securities
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Total	751,974
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Estimated Fair Value	761,153	648,471
Available for Sale Securities Weighted Avg Yield	2.36%
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
U.S. Government sponsored entities’ asset-backed securities	140,562	181,821
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
U.S. Government sponsored entities’ asset-backed securities	$ 143,490	$ 187,161
Held to Maturity Securities weighted avg yield	3.58%

Available for Sale Securities Debt Maturities After Five Through Ten Years Weighted Avg Yield

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Available for Sale Securities Debt Maturities After One Through Five Years Weighted Avg Yield

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Available for Sale Securities Weighted Avg Yield

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Held to Maturity Securities weighted avg yield

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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-Publisher FASB

-Name Accounting Standards Codification

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

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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

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