Securities - Summary of amortized cost and fair value by contractual maturity of securities available for sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Total availible-for-sale securities, Amortized Cost	$ 77,246	$ 77,773
Total availible-for-sale securities, Fair Value	75,434	77,153	[1]
State and Municipal Obligations
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	1,240	1,241
Due after one year but less than five years, Amortized Cost	7,987	7,173
Due after five years but less than ten years, Amortized Cost	11,356	11,736
Due after ten years, Amortized Cost	481	963
Total availible-for-sale securities, Amortized Cost	21,064	21,113
Due in one year or less, Fair Value	1,236	1,237
Due after one year but less than five years, Fair Value	7,931	7,219
Due after five years but less than ten years, Fair Value	11,063	11,740
Due after ten years, Fair Value	467	957
Total availible-for-sale securities, Fair Value	20,697	21,153
US Government Agencies Agencies and Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Total availible-for-sale securities, Amortized Cost	49,086	49,964
Total availible-for-sale securities, Fair Value	47,622	49,283
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Total availible-for-sale securities, Amortized Cost	7,096	6,696
Total availible-for-sale securities, Fair Value	$ 7,115	$ 6,717

[1] Derived from the audited December 31, 2017 Consolidated Financial Statements.