Securities - Maturities of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of debt securities available for sale, due within one year	$ 4,830	$ 4,830
Amortized cost of debt securities available for sale, due in one to five years	16,675	21,564
Amortized cost of debt securities available for sale, due in five to ten years	40,668	41,683
Amortized cost of debt securities available for sale, due after ten years	26,089	33,119
Total amortized cost debt securities available for sale with specific maturities	88,262	101,196
Amortized Cost	243,151	297,848
Estimated fair value of debt securities available for sale, due within one year	4,927	4,927
Estimated fair value of debt securities available for sale, due in one to five years	16,972	21,818
Estimated fair value of debt securities available for sale, due in five to ten years	41,210	42,613
Estimated fair value of debt securities available for sale, due after ten years	27,452	35,380
Total estimated fair value of debt securities available for sale with specific maturities	90,561	104,738
Total unrestricted securities available for sale at estimated fair value	247,673	303,628
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost of debt securities available for sale without specific maturities	89,386	119,347
Total estimated fair value of debt securities available for sale without specific maturities	89,890	119,810
Amortizing Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost of debt securities available for sale without specific maturities	65,503	77,305
Total estimated fair value of debt securities available for sale without specific maturities	$ 67,222	$ 79,080