Securities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended							12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Gain on sale of securities	$ 52	$ (146)	$ (65)	$ 100	$ 2,148	$ 5,392	$ 1,729	$ (59)	$ 9,269	$ 1,641
Council Oak Investment Corporation [Member]
Schedule of Available-for-sale Securities [Line Items]
Pretax gain on sale of equity investments									1,700
Council Oak Partners [Member]
Schedule of Available-for-sale Securities [Line Items]
Pretax gain on sale of equity investments									5,200
Gain on sale of securities									$ 2,100