Condensed Financial Information - Parent Company Only - 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
Statements of Income
Net gain on sales of investment securities									$ 518	$ 1,265	$ 635
Income before income taxes	$ 7,486	$ (1,475)	$ 7,286	$ 10,089	$ 9,711	$ 10,307	$ 8,758	$ 8,250	23,386	37,026	29,679
Income taxes	568	(1,533)	2,046	2,800	2,553	2,779	2,292	2,134	3,881	9,758	7,448
Equity in undistributed (loss) income of subsidiaries:
Net income	$ 6,918	$ 58	$ 5,240	$ 7,289	$ 7,158	$ 7,528	$ 6,466	$ 6,116	19,505	27,268	22,231
Parent Company [Member]
Statements of Income
Dividends from Bank									94,042	26,523	12,482
Dividends from non-bank									0	0	0
Net gain on sales of investment securities									23	285	306
Other income									18,663	18,428	18,334
Total operating income									112,728	45,236	31,122
Operating expenses									30,001	21,833	16,924
Income before income taxes									82,727	23,403	14,198
Income taxes									(3,834)	(728)	880
Income before equity in undistributed (loss) income of subsidiaries									86,561	24,131	13,318
Equity in undistributed (loss) income of subsidiaries:
Bank									(67,056)	3,137	8,913
Non-banks									0	0	0
Net income									$ 19,505	$ 27,268	$ 22,231