Investment Securities - Summary of Amortized Cost and Estimated Fair Values of Securities Held to Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Amortized Cost	$ 20,335	$ 33,258
Gross Unrealized Gains	416	592
Gross Unrealized Losses	842	2,672
Estimated Fair Value	19,909	31,178
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Investments [Line Items]
Amortized Cost	5,215	5,295
Gross Unrealized Gains	400	570
Gross Unrealized Losses	0	0
Estimated Fair Value	5,615	5,865
State and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Amortized Cost	5,674	8,598
Gross Unrealized Gains	12	17
Gross Unrealized Losses	0	0
Estimated Fair Value	5,686	8,615
Residential Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Amortized Cost	26	30
Gross Unrealized Gains	4	5
Gross Unrealized Losses	0	0
Estimated Fair Value	30	35
Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	9,400	19,315
Gross Unrealized Gains	0	0
Gross Unrealized Losses	842	2,672
Estimated Fair Value	8,558	16,643
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Amortized Cost	20	20
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 20	$ 20