Securities - Summary of Amortized Cost and Estimated Fair Values of Securities Held for Investment (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,942	$ 4,365
Gross Unrealized Gains	34	42
Gross Unrealized Losses	(1)	(4)
Estimated Fair Value	3,975	4,403
Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	217	252
Gross Unrealized Gains	12	17
Estimated Fair Value	229	269
States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,225	3,613
Gross Unrealized Gains	22	25
Gross Unrealized Losses	(1)	(4)
Estimated Fair Value	3,246	3,634
Other Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	500	500
Estimated Fair Value	$ 500	$ 500