Securities - Components of Available for Sale Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 493,067	$ 506,429
Available-for-sale securities, Gross unrealized gains	1,717	515
Available-for-sale securities, Gross unrealized losses	(2,372)	(7,154)
Total fair value	492,412us-gaap_AvailableForSaleSecurities	499,790us-gaap_AvailableForSaleSecurities
U.S. Treasury and Government Sponsored Entities' Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	226,812	232,225
Available-for-sale securities, Gross unrealized gains	947	184
Available-for-sale securities, Gross unrealized losses	(866)	(4,452)
Total fair value	226,893	227,957
Mortgage-Backed GSE Securities: Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	266,255	274,204
Available-for-sale securities, Gross unrealized gains	770	331
Available-for-sale securities, Gross unrealized losses	(1,506)	(2,702)
Total fair value	$ 265,519	$ 271,833

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

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity 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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