Summary of Quarterly Results of Operations (Unaudited) - Result of Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended							9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2014	Sep. 30, 2013
Loans:
Discount accretion PCI - cash basis	$ 290	$ 69	$ 203	$ 255	$ 140	$ 129	$ 167
Discount accretion PCI - other	822	811	984	893	898	732	597
Discount accretion PNCI	402	624	379	568	1,115	815	766
All other loan interest income	23,466	22,929	22,172	22,754	22,970	22,207	22,542
Total loan interest income	24,980	24,433	23,738	24,470	25,123	23,883	24,072
Debt securities, dividends and interest bearing cash at Banks (not FTE)	4,151	3,985	3,421	2,992	2,413	1,873	1,734
Total interest and dividend income	29,131	28,418	27,159	27,462	27,536	25,756	25,806	84,708	79,098
Interest expense	1,082	1,075	1,087	1,123	1,169	1,167	1,237	3,244	3,573
Net interest income	28,049	27,343	26,072	26,339	26,367	24,589	24,569	81,464	75,525
(Benefit from) provision for loan losses	(2,977)	1,708	(1,355)	172	(393)	614	(1,108)	(2,624)	(887)
Net interest income after provision for loan losses	31,026	25,635	27,427	26,167	26,760	23,975	25,677	84,088	76,412
Noninterest income	8,589	7,877	8,295	7,353	9,127	10,131	10,218	24,761	29,476
Noninterest expense	25,380	25,116	23,317	24,878	23,616	23,509	21,601	73,813	68,726
Income before income taxes	14,235	8,396	12,405	8,642	12,271	10,597	14,294	35,036	37,162
Income tax expense	6,001	3,537	5,040	3,406	4,910	4,272	5,817	14,578	14,999
Net income	$ 8,234	$ 4,859	$ 7,365	$ 5,236	$ 7,361	$ 6,325	$ 8,477	$ 20,458	$ 22,163
Per common share:
Net income (diluted)	$ 0.50	$ 0.30	$ 0.45	$ 0.32	$ 0.45	$ 0.39	$ 0.53	$ 1.25	$ 1.37
Dividends	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.09