Short-Term Borrowings - Summary of Federal Funds Purchased and Other Short-term Borrowings (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Average balance		$ 69,000
Average rate paid		0.53%
Short Term Borrowings [Member]
Short-term Debt [Line Items]
Outstanding balance		$ 53,700,000
Maximum indebtedness	$ 70,400,000	64,700,000
Average balance	$ 20,571,000	$ 26,880,000
Average rate paid	0.39%	0.20%
Interest rate on balance		0.35%