Securities - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
Securities pledged for public funds	$ 150,600,000		$ 150,600,000		$ 107,100,000
Available for sale securities transferred to held to maturity, total amortized cost		$ 105,300,000
Available for sale securities transferred to held to maturity fair value		103,800,000
Net unrealized loss, net of taxes, on securities at date of transfer		(999,000)
Proceeds from the sale of securities available for sale	5,200,000	0	33,702,000	$ 5,153,000
Gross gains realized on sales of securities available for sale	218,000	0	604,000	11,000
Income tax expense related to net realized gains	$ 76,000	$ 0	$ 211,000	$ 4,000