Condensed Parent Company Financial Statements - Schedule of Condensed Income Statement (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	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Income Statements, Captions [Line Items]
Income from securities	$ 80,819	$ 70,092	$ 67,585	$ 67,601	$ 67,660	$ 66,935	$ 66,729	$ 60,379	$ 286,097	$ 261,712	$ 215,991
Net securities gain									2,357	948	903
Other income									9,751	5,532	5,555
Interest expense	9,131	8,066	7,811	7,759	7,040	6,326	5,936	5,424	32,767	24,725	22,763
Other expense									41,000	38,887	37,196
Total non-interest expense	58,298	57,601	47,360	45,343	46,894	46,981	46,589	53,441	208,680	193,923	161,633
Income tax benefit	8,464	5,793	8,085	8,694	8,165	7,768	7,962	4,528	31,036	28,415	23,720
NET INCOME	$ 24,218	$ 17,435	$ 22,109	$ 22,874	$ 23,002	$ 22,248	$ 21,633	$ 13,887	86,635	80,762	69,974
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Dividends from subsidiaries - Bank									85,000	60,000	59,500
Dividends from subsidiaries - Nonbank									800	500	1,200
Income from securities									75	75	128
Net securities gain											745
Other income									147	104	416
Total income									86,022	60,679	61,989
Interest expense									4,136	3,315	3,199
Other expense									5,628	5,547	3,940
Total non-interest expense									9,764	8,862	7,139
Income before income tax benefit and undistributed net income of subsidiaries									76,258	51,817	54,850
Income tax benefit									(3,149)	(2,971)	(2,006)
Income before undistributed net income of subsidiaries									79,407	54,788	56,856
Equity in undistributed net income of subsidiaries									7,228	25,974	13,118
NET INCOME									$ 86,635	$ 80,762	$ 69,974