Quarterly Financial Data (Unaudited) - Schedule of Consolidated Quarterly Financial Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected Income Statement Data:
Interest income	$ 44,900	$ 43,186	$ 38,607	$ 37,873	$ 31,749	$ 31,749	$ 31,951	$ 30,873	$ 164,566	$ 126,322	$ 129,479
Interest expense	3,894	4,054	3,343	3,389	2,698	2,429	2,475	2,535	14,680	10,137	15,074
Net interest income	41,006	39,132	35,264	34,484	29,051	29,320	29,476	28,338	149,886	116,185	114,405
Provision for loan losses	888	1,669	1,365	1,726	1,478	2,920	4,165	2,923	5,648	11,486	31,089
Net interest income after provision for loan losses	40,118	37,463	33,899	32,758	27,573	26,400	25,311	25,415	144,238	104,699	83,316
Noninterest income	16,362	17,901	15,819	12,754	11,517	12,288	11,384	11,360	62,836	46,549	57,874
Noninterest expense	41,666	38,028	34,446	32,789	33,274	28,237	26,688	28,884	150,869	121,945	119,470
Acquisition related expenses	67	551	2,872	450	4,350	512
Income before income tax expense	14,747	16,785	12,400	12,273	1,466	9,939	10,007	7,891	56,205	29,303	21,720
Income tax	4,167	5,122	4,270	3,923	88	3,262	3,329	2,606	17,482	9,285	7,285
Net income	10,580	11,663	8,130	8,350	1,378	6,677	6,678	5,285	38,723	20,018	14,435
Preferred stock dividends				286	412	443	442	441	286	1,738	3,577
Net income available to common stockholders	$ 10,580	$ 11,663	$ 8,130	$ 8,064	$ 966	$ 6,234	$ 6,236	$ 4,844	$ 38,437	$ 18,280	$ 10,858
Per Share Data:
Net income - basic	$ 0.40	$ 0.44	$ 0.32	$ 0.32	$ 0.04	$ 0.26	$ 0.26	$ 0.20	$ 1.48	$ 0.76	$ 0.46
Net income - diluted	$ 0.39	$ 0.43	$ 0.32	$ 0.32	$ 0.04	$ 0.26	$ 0.26	$ 0.20	$ 1.46	$ 0.75	$ 0.46
Common Dividends (Cash)	$ 0.05	$ 0.05	$ 0.05
Common Dividends (Stock)	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0.15