Condensed Financial Information - Parent Company Only - Schedule of Condensed Income Statement (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statements of Income
Net gain on sales of investment securities									$ 1,265	$ 635	$ 3,389
Loss on termination of interest rate swap									0	0	(1,866)
Income before income taxes	$ 9,711	$ 10,307	$ 8,758	$ 8,250	$ 6,822	$ 8,499	$ 6,627	$ 7,731	37,026	29,679	26,885
Income taxes	2,553	2,779	2,292	2,134	1,632	2,264	1,547	2,005	9,758	7,448	5,696
Equity in undistributed income (loss) of subsidiaries:
Net income	$ 7,158	$ 7,528	$ 6,466	$ 6,116	$ 5,190	$ 6,235	$ 5,080	$ 5,726	27,268	22,231	21,189
Parent Company [Member]
Statements of Income
Dividends from Bank									26,523	12,482	18,482
Dividends from non-bank									0	0	0
Net gain on sales of investment securities									285	306	644
Loss on termination of interest rate swap									0	0	(1,866)
Other income									18,428	18,334	18,306
Total operating income									45,236	31,122	35,566
Operating expenses									21,833	16,924	19,203
Income before income taxes									23,403	14,198	16,363
Income taxes									(728)	880	(903)
Income before equity in undistributed income (loss) of subsidiaries									24,131	13,318	17,266
Equity in undistributed income (loss) of subsidiaries:
Bank									3,137	8,913	3,929
Non-banks									0	0	(6)
Net income									$ 27,268	$ 22,231	$ 21,189