Summary of Quarterly Results of Operations (Unaudited) - Result of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015
Loans:
Discount accretion PCI - cash basis	$ 426	$ 269	$ 302	$ 445	$ 404	$ 172
Discount accretion PCI - other	415	(45)	1,392	1,090	907	1,274
Discount accretion PNCI	1,459	868	573	1,590	822	1,348
All other loan interest income	32,038	33,646	32,571	30,689	29,886	28,371
Total loan interest income	34,338	34,738	34,838	33,814	32,019	31,165	$ 69,076	$ 63,184
Debt securities, dividends and interest bearing cash at banks (not FTE)	8,252	8,056	7,652	7,518	7,848	6,560
Total interest and dividend income	42,590	42,794	42,490	41,332	39,867	37,725	85,384	77,592
Interest expense	1,430	1,392	1,349	1,339	1,346	1,382	2,822	2,728
Net interest income	41,160	41,402	41,141	39,993	38,521	36,343	82,562	74,864
(Benefit from reversal of) provision for loan losses	(773)	209	(908)	(866)	(633)	197	(564)	(436)
Net interest income after provision for loan losses	41,933	41,193	42,049	40,859	39,154	36,146	83,126	75,300
Noninterest income	11,245	9,790	11,445	11,642	12,080	10,180	21,035	22,260
Noninterest expense	38,267	33,751	34,684	31,439	32,436	32,282	72,018	64,718
Income before income taxes	14,911	17,232	18,810	21,062	18,798	14,044	32,143	32,842
Income tax expense	5,506	6,558	7,388	8,368	7,432	5,708	12,064	13,140
Net income	$ 9,405	$ 10,674	$ 11,422	$ 12,694	$ 11,366	$ 8,336	$ 20,079	$ 19,702
Per common share:
Net income (diluted)	$ 0.41	$ 0.46	$ 0.50	$ 0.55	$ 0.49	$ 0.36	$ 0.87	$ 0.86
Dividends	$ 0.15	$ 0.15	$ 0.15	$ 0.13	$ 0.13	$ 0.11	$ 0.30	$ 0.24