Securities - Summary of Amortized Cost and Estimated Fair Values of Securities Held for Investment (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 4,554	$ 8,789
Gross Unrealized Gains	49	61
Gross Unrealized Losses	(2)
Estimated Fair Value	4,601	8,850
Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	273	347
Gross Unrealized Gains	21	25
Estimated Fair Value	294	372
States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,781	7,942
Gross Unrealized Gains	28	36
Gross Unrealized Losses	(2)
Estimated Fair Value	3,807	7,978
Other Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	500	500
Estimated Fair Value	$ 500	$ 500