Derivative Instruments - Amounts and Locations of Activity Related to Back-to-Back Interest Rate Swaps within Corporation's Consolidated Balance Sheet (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
3rd Party Interest Rate Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Notional Amount	$ 9,443,000	$ 6,751,000
Average Maturity (in years)	9 years 7 months 6 days	9 years 4 months 24 days
Weighted Average Fixed Rate	4.31%	4.42%
Weighted Average Variable Rate, Description	1 month LIBOR +2.25%
Weighted Average Variable Rate	2.25%	2.25%
Fair Value	$ 462,000	$ 131,000
Customer Interest Rate Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Notional Amount	$ (9,443,000)	$ (6,751,000)
Average Maturity (in years)	9 years 7 months 6 days	9 years 4 months 24 days
Weighted Average Fixed Rate	4.31%	4.42%
Weighted Average Variable Rate, Description	1 month LIBOR +2.25%
Weighted Average Variable Rate	2.25%	2.25%
Fair Value	$ (462,000)	$ (131,000)