Securities - Summary of Amortized Cost and Estimated Fair Values of Securities Held for Investment (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 8,333	$ 8,593
Gross Unrealized Gains	65	78
Estimated Fair Value	8,398	8,671
Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	382	471
Gross Unrealized Gains	30	34
Estimated Fair Value	412	505
States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	7,951	8,122
Gross Unrealized Gains	35	44
Estimated Fair Value	$ 7,986	$ 8,166