Loans - Additional Information (Detail)		3 Months Ended		12 Months Ended
	Dec. 31, 2015 USD ($) Loans SecurityLoan	Mar. 31, 2016 USD ($) Loans SecurityLoan	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentrations of loans exceeding 10% of total loans | Loans	0	0		0
Allowance for loan losses	$ 5,700,000	$ 6,163,000	$ 6,200,000	$ 5,700,000
Ratio of the allowance for loan losses to total loans		1.10%	1.11%	1.01%
Company's annualized net charge off (net recovery) ratios		0.00%	0.24%	0.29%
Ratios of allowance for loan losses to non-accrual loans	76.80%	122.54%	290.51%	76.80%
Annual reviews of loan to ascertain the borrowers continued ability to service		$ 1,000,000
Loans past due period for classify to risk grade		90 days
Total impaired loans Recorded Investment	$ 28,074,000	$ 27,462,000	$ 31,900,000	$ 28,074,000
Reserve on impaired loans	$ 630,000	$ 765,000	$ 1,800,000	630,000
Number of additional TDRs | SecurityLoan	8	4
Number of lending relationships | SecurityLoan	2	1
Maximum interest payment period under TDRs		1 year
Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reserve on impaired loans	$ 69,000	$ 108,000		$ 69,000
Impaired Loans Substandard [Member] | Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Substandard land loan		$ 7,121