Securities - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) Securities	Mar. 31, 2017	Dec. 31, 2017 USD ($) Securities
Schedule of Available-for-sale Securities [Line Items]
Average taxable equivalent yields on securities	2.68%	3.22%
Fair value of securities	$ 19,100		$ 19,400
Securities sold under repurchase agreements	6,551		9,498	[1]
Company's investment in Federal Home Loan Bank stock	3,400		3,700
Company's investment in Federal Reserve Bank stock	$ 1,900		$ 1,900
U.S. Government Agencies
Schedule of Available-for-sale Securities [Line Items]
Securities with unrealized loss positions | Securities	40		36
State and Municipal Obligations
Schedule of Available-for-sale Securities [Line Items]
Securities with unrealized loss positions | Securities	48		34
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Securities with unrealized loss positions | Securities			1

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