Short-Term Borrowings - Summary of Federal Funds Purchased and Other Short-term Borrowings (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Maximum indebtedness	$ 20,000,000
Average balance	$ 157,000	$ 69,000
Average rate paid	0.79%	0.53%
Short Term Borrowings [Member]
Short-term Debt [Line Items]
Outstanding balance	$ 17,500,000	$ 53,700,000
Maximum indebtedness	70,400,000	64,700,000
Average balance	$ 13,290,000	$ 26,880,000
Average rate paid	0.42%	0.20%
Interest rate on balance	0.40%	0.35%