Summary of Quarterly Results of Operations (Unaudited) - Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended							9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
Loans:
Discount accretion PCI - cash basis	$ 398	$ 386	$ 112	$ 483	$ 777	$ 426	$ 269
Discount accretion PCI - other	407	797	631	658	569	415	(45)
Discount accretion PNCI	559	987	798	637	883	1,459	868
All other loan interest income	35,904	34,248	33,373	34,463	33,540	32,038	33,646
Total loan interest income	37,268	36,418	34,914	36,241	35,769	34,338	34,738	$ 108,600	$ 104,845
Debt securities, dividends and interest bearing cash at Banks (not FTE)	8,645	8,626	8,570	8,374	7,940	8,252	8,056
Total interest and dividend income	45,913	45,044	43,484	44,615	43,709	42,590	42,794	134,441	129,093
Interest expense	1,829	1,610	1,491	1,460	1,439	1,430	1,392	4,930	4,261
Net interest income	44,084	43,434	41,993	43,155	42,270	41,160	41,402	129,511	124,832
(Benefit from reversal of) provision for loan losses	765	(796)	(1,557)	(1,433)	(3,973)	(773)	209	(1,588)	(4,537)
Net interest income after provision for loan losses	43,319	44,230	43,550	44,588	46,243	41,933	41,193	131,099	129,369
Noninterest income	12,930	12,910	11,703	12,462	11,066	11,245	9,790	37,543	32,101
Noninterest expense	37,222	35,904	35,822	36,563	37,416	38,267	33,751	108,948	109,434
Income before income taxes	19,027	21,236	19,431	20,487	19,893	14,911	17,232	59,694	52,036
Income tax expense	7,130	7,647	7,352	7,954	7,694	5,506	6,558	22,129	19,758
Net income	$ 11,897	$ 13,589	$ 12,079	$ 12,533	$ 12,199	$ 9,405	$ 10,674	$ 37,565	$ 32,278
Per common share:
Net income (diluted)	$ 0.51	$ 0.58	$ 0.52	$ 0.54	$ 0.53	$ 0.41	$ 0.46	$ 1.62	$ 1.40
Dividends	$ 0.17	$ 0.17	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.49	$ 0.45