Summary of Quarterly Results of Operations (Unaudited) - Result of Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Loans:
Discount accretion PCI - cash basis	$ 172	$ 107	$ 290	$ 69	$ 203
Discount accretion PCI - other	1,274	919	822	811	984
Discount accretion PNCI	1,348	796	402	624	379
All other loan interest income	28,371	28,914	23,466	22,929	22,172
Total loan interest income	31,165	30,736	24,980	24,433	23,738
Debt securities, dividends and interest bearing cash at Banks (not FTE)	6,560	5,671	4,151	3,985	3,421
Total interest and dividend income	37,725	36,407	29,131	28,418	27,159
Interest expense	1,382	1,437	1,082	1,075	1,087
Net interest income	36,343	34,970	28,049	27,343	26,072
(Benefit from) provision for loan losses	197	(1,421)	(2,977)	1,708	(1,355)
Net interest income after provision for loan losses	36,146	36,391	31,026	25,635	27,427
Noninterest income	10,180	9,755	8,589	7,877	8,295
Noninterest expense	32,282	36,566	25,380	25,116	23,317
Income before income taxes	14,044	9,580	14,235	8,396	12,405
Income tax expense	5,708	3,930	6,001	3,537	5,040
Net income	$ 8,336	$ 5,650	$ 8,234	$ 4,859	$ 7,365
Per common share:
Net income (diluted)	$ 0.36	$ 0.25	$ 0.50	$ 0.30	$ 0.45
Dividends	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11