Summary of Quarterly Results of Operations (Unaudited) - Result of Operations (Detail) - USD ($) $ / shares in Units, $ 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
Loans:
Discount accretion PCI - cash basis	$ 483	$ 777	$ 426	$ 269	$ 302	$ 445	$ 404	$ 172
Discount accretion PCI - other	658	569	415	(45)	1,392	1,090	907	1,274
Discount accretion PNCI	637	883	1,459	868	573	1,590	822	1,348
All other loan interest income	34,463	33,540	32,038	33,646	32,571	30,689	29,886	28,371
Total loan interest income	36,241	35,769	34,338	34,738	34,838	33,814	32,019	31,165	$ 141,086	$ 131,836	$ 103,887
Debt securities, dividends and interest bearing cash at banks (not FTE)	8,374	7,940	8,252	8,056	7,652	7,518	7,848	6,560
Total interest and dividend income	44,615	43,709	42,590	42,794	42,490	41,332	39,867	37,725	173,708	161,414	121,115
Interest expense	1,460	1,439	1,430	1,392	1,349	1,339	1,346	1,382	5,721	5,416	4,681
Net interest income	43,155	42,270	41,160	41,402	41,141	39,993	38,521	36,343	167,987	155,998	116,434
(Benefit from reversal of) provision for loan losses	(1,433)	(3,973)	(773)	209	(908)	(866)	(633)	197	(5,970)	(2,210)	(4,045)
Net interest income after provision for loan losses	44,588	46,243	41,933	41,193	42,049	40,859	39,154	36,146	173,957	158,208	120,479
Noninterest income	12,462	11,066	11,245	9,790	11,445	11,642	12,080	10,180	44,563	45,347	34,516
Noninterest expense	36,563	37,416	38,267	33,751	34,684	31,439	32,436	32,282	145,997	130,841	110,379
Income before income taxes	20,487	19,893	14,911	17,232	18,810	21,062	18,798	14,044	72,523	72,714	44,616
Income tax expense	7,954	7,694	5,506	6,558	7,388	8,368	7,432	5,708	27,712	28,896	18,508
Net income	$ 12,533	$ 12,199	$ 9,405	$ 10,674	$ 11,422	$ 12,694	$ 11,366	$ 8,336	$ 44,811	$ 43,818	$ 26,108
Per common share:
Net income (diluted)	$ 0.54	$ 0.53	$ 0.41	$ 0.46	$ 0.50	$ 0.55	$ 0.49	$ 0.36	$ 1.94	$ 1.91	$ 1.46
Dividends	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.13	$ 0.13	$ 0.11	$ 0.60	$ 0.52	$ 0.44