Securities - Additional Information (Detail) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
Securities pledged for public funds	$ 155,500,000			$ 155,500,000		$ 107,100,000
Securities available for sale, less than twelve months	0			0		240,461,000
Securities available for sale, twelve months or more	0			0		69,333,000
Unrealized loss, less than twelve months	0			0		2,496,000
Unrealized loss, twelve months or more	0			0		$ 1,743,000
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	10,400,000		$ 0	28,530,000	$ 5,153,000
Gross gains realized on sales of securities available for sale	233,000		0	386,000	11,000
Income tax expense related to net realized gains	$ 81,000		$ 0	$ 135,000	$ 4,000