Derivative Instruments - Additional Information (Detail) - USD ($)		6 Months Ended
	May 03, 2011	Jun. 30, 2018	Dec. 31, 2017
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Term of agreement	5 years
Derivatives designated as fair value hedges		$ 0	$ 0
Accumulated other comprehensive loss estimated		171,000
Collateral amount for counterparty interest rate swap		$ 1,400,000	1,400,000
LIBOR Plus 155 Basis Points
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Variable interest rate on subordinate debt		3.89%
Derivative basis spread on variable rate		1.55%
4.02% Fixed Rate Plus 155 Basis Points
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Variable interest rate on subordinate debt		5.57%
Derivative fixed interest rate rate basis		4.02%
Interest Rate Swaps
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Cash collateral pledged		$ 750,000	$ 750,000
LIBOR | 4.02% Fixed Rate Plus 155 Basis Points
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative basis spread on variable rate		1.55%
Unsecured Debt
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Subordinated note	$ 10,000,000