Loans - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of outstanding principal balances of commercial real estate loans secured by owner-occupied properties	76.00%		76.00%
Loans serviced for others	$ 80,200,000		$ 76,300,000
Concentrations of loans related to a single industry	0		0
Loans classified as troubled debt restructurings	6,700,000		7,600,000
Reserves allocated to customers whose loan terms are modified in troubled debt restructurings	26,000		26,000
Loans payable in nonaccrual of interest status	409,000
Foreclosed real estate	0		0
Consumer mortgage loans in process of foreclosure amount	360,000		$ 89,000
Loans restructured, subsequently defaulted	0	$ 0
Outstanding balance of commercial loans classified under credit risk, minimum amount	300,000
Loans listed as not rated under risk category, maximum amount	300,000
Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans classified as troubled debt restructurings	$ 6,300,000