Interest Rate Swaps - Amounts and Locations of Activity Related to Back-to-Back Interest Rate Swaps (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
3rd Party interest rate swaps
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Notional Amount, Asset	$ 23,152	$ 11,848
Average Maturity (in years)	7 years 2 months 12 days	8 years
Weighted Average Fixed Rate	3.85%	4.51%
Assets (Liabilities), at fair value	$ 485	$ 149
Customer interest rate swaps
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Notional Amount, Liability	$ (23,152)	$ (11,848)
Average Maturity (in years)	7 years 2 months 12 days	8 years
Weighted Average Fixed Rate	3.85%	4.51%
Assets (Liabilities), at fair value	$ (485)	$ (149)
LIBOR | 3rd Party interest rate swaps
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative basis spread on variable rate	2.24%	2.37%
LIBOR | Customer interest rate swaps
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative basis spread on variable rate	2.24%	2.37%