Securities - Amortized Cost and Fair Value of Securities Available for Sale and Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized cost within one year	$ 3,968	$ 4,358
Amortized cost one to five years	49,167	49,415
Amortized cost for five to ten years	99,931	98,551
Amortized cost for after ten years	67,338	61,313
Total amortized cost	220,404	213,637
Total available for sale investment securities, Amortized Cost	509,840	463,306
Within one year, amortized cost	9,910
One to five years, amortized cost
Total held to maturity investment securities, amortized cost	9,910
Fair value within one year	3,987	4,368
Fair value for one to five years	49,763	50,673
Fair value for five to ten years	102,194	104,258
Fair value for after ten years	66,890	65,436
Total fair value	222,834	224,735
Investment securities, available for sale	514,144	482,801
Within one year, fair value	9,910
One to five years, fair value
Held-to-maturity, fair value	9,910
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	111,266	95,337
Investment securities, available for sale	110,782	96,831
Federal Agency Mortgage-Backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	176,880	152,372
Investment securities, available for sale	179,194	159,204
Private Labeled Mortgage-Backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	1,290	1,960
Investment securities, available for sale	$ 1,334	$ 2,031

Available for sale securities debt maturities rolling fair value.

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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 of available-for-sale debt securities at cost, net of adjustments, which include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the next rolling twelve months following the latest balance sheet presented. 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, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at fair value maturing in the next rolling twelve months following the latest balance sheet presented.

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Amount of available-for-sale debt securities at cost, net of adjustments, maturing after the tenth rolling twelve months following the latest balance sheet presented. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at fair value maturing after the tenth rolling twelve months following the latest balance sheet presented.

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Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the sixth rolling twelve months through the tenth rolling twelve months following the latest balance sheet presented. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at fair value maturing in the sixth rolling twelve months through the tenth rolling twelve months following the latest balance sheet presented.

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Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the second rolling twelve months through the fifth rolling twelve months following the latest balance sheet presented. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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Amount of available-for-sale debt securities at fair value maturing in the second rolling twelve months through the fifth rolling twelve months following the latest balance sheet presented.

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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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Carrying amount of debt securities accounted for as held-to-maturity, net of adjustments including, but not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized, and fair value hedge accounting adjustments, maturing in the next fiscal year through the fifth fiscal year following the latest fiscal year.

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Amount of held-to-maturity debt securities at fair value maturing in the next rolling twelve months following the latest balance sheet presented.

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Amount of held-to-maturity debt securities at fair value maturing in the second rolling twelve months through the fifth rolling twelve months following the latest balance sheet presented.

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

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