Securities - Summary of Amortized Cost and Estimated Fair Values of Securities Held for Investment (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 4,365	$ 8,789
Gross Unrealized Gains	42	61
Gross Unrealized Losses	(4)
Estimated Fair Value	4,403	8,850
Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	252	347
Gross Unrealized Gains	17	25
Estimated Fair Value	269	372
States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,613	7,942
Gross Unrealized Gains	25	36
Gross Unrealized Losses	(4)
Estimated Fair Value	3,634	7,978
Other Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	500	500
Estimated Fair Value	$ 500	$ 500