Summary of Significant Accounting Policies - Additional Information (Detail)			3 Months Ended		12 Months Ended
	Mar. 24, 2016 USD ($) $ / shares shares	Mar. 15, 2016	Mar. 31, 2016 USD ($) $ / shares	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 $ / shares
Accounting Policies [Abstract]
Shares of common stock issued per share held in stock split		1.3333
Common stock issued for stock split (in shares) | shares	2,564,091
Common stock, par value (in dollars per share) | $ / shares	$ 2.00		$ 2.00			$ 2.0
Adjustments to common stock and additional paid-in capital, stock split	$ 5,102,000
Minimum past due of loans for nonaccrual status			90 days
Loans with identified weakness and principal balance				$ 500,000	$ 100,000
Assignment of valuation allowance for specified amount of loan (less than)			$ 500,000