Investment Securities - Schedule of Amortized Cost and Approximate Fair Value of Investment Debt Securities by Contractual Maturity (Including Mortgage-backed Securities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Amortized Cost And Fair Value Debt Securities [Abstract]
Weighted Average T.E. Yield of Securities Available-For-Sale, Due within one year	1.31%
Weighted Average T.E. Yield of Securities Available-For-Sale, Due after one year through five years	2.17%	2.01%
Weighted Average T.E. Yield of Securities Available-For-Sale, Due after five years through ten years	2.79%	2.81%
Weighted Average T.E. Yield of Securities Available-For-Sale, Due after ten years	2.43%	2.63%
Amortized Cost of Securities Available-For-Sale, Due within one year	$ 859
Amortized Cost of Securities Available-For-Sale, Due after one year through five years	10,132	$ 9,979
Amortized Cost of Securities Available-For-Sale, Due after five years through ten years	25,354	23,662
Amortized Cost of Securities Available-For-Sale, Due after ten years	110,468	79,003
Amortized Cost of Total debt securities	146,813	112,644
Fair Value of Securities Available-For-Sale, Due within one year	858
Fair Value of Securities Available-For-Sale, Due after one year through five years	10,154	9,984
Fair Value of Securities Available-For-Sale, Due after five years through ten years	25,447	23,494
Fair Value of Securities Available-For-Sale, Due after ten years	111,785	78,801
Fair Value of Total Debt Securities Available-For-Sale	$ 148,244	$ 112,279
Weighted Average T.E. Yield of Securities Held-To-Maturity, Due within one year	7.17%	7.17%
Weighted Average T.E. Yield of Securities Held-To-Maturity, Due after one year through five years	7.17%	7.17%
Weighted Average T.E. Yield of Securities Held-To-Maturity, Due after five years through ten years	7.17%	7.17%
Weighted Average T.E. Yield of Securities Held-To-Maturity, Due after ten years	3.41%	3.17%
Amortized Cost of Securities Held-To-Maturity, Due within one year	$ 655	$ 655
Amortized Cost of Securities Held-To-Maturity, Due after one year through five years	2,950	2,950
Amortized Cost of Securities Held-To-Maturity, Due after five years through ten years	3,575	3,575
Amortized Cost of Securities Held-To-Maturity, Due after ten years	14,274	19,228
Amortized Cost	21,454	26,408
Fair Value of Securities Held-To-Maturity, Due within one year	657	657
Fair Value of Securities Held-To-Maturity, Due after one year through five years	2,957	2,958
Fair Value of Securities Held-To-Maturity, Due after five years through ten years	3,583	3,584
Fair Value of Securities Held-To-Maturity, Due after ten years	14,428	19,072
Fair Value of Total Debt Securities Held-To-Maturity	$ 21,625	$ 26,271