Securities - Components of Available for Sale Portfolio (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 482,760	$ 506,429
Available-for-sale securities, Gross unrealized gains	218	515
Available-for-sale securities, Gross unrealized losses	(10,006)	(7,154)
Total fair value	472,972	499,790
U.S. Treasury and Government Sponsored Entities' Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	226,539	232,225
Available-for-sale securities, Gross unrealized gains	125	184
Available-for-sale securities, Gross unrealized losses	(5,569)	(4,452)
Total fair value	221,095	227,957
Mortgage-Backed GSE Securities: Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	256,221	274,204
Available-for-sale securities, Gross unrealized gains	93	331
Available-for-sale securities, Gross unrealized losses	(4,437)	(2,702)
Total fair value	$ 251,877	$ 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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