Segment Reporting - Schedule of Financial Information with Respect to Company's Reportable Business Segments (Detail) (USD $) In Thousands, 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
Segment Reporting Information [Line Items]
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
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:
Salaries and employee benefits									73,878	56,670	53,122
Equipment and occupancy expenses									17,521	12,286	13,208
Data processing and telecommunications expenses									15,551	11,539	10,683
Other expenses									43,919	41,450	42,457
Total noninterest expense	41,666	38,028	34,446	32,789	33,274	28,237	26,688	28,884	150,869	121,945	119,470
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 expense	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
Less preferred stock dividends				286	412	443	442	441	286	1,738	3,577
Net income available to common shareholders	10,580	11,663	8,130	8,064	966	6,234	6,236	4,844	38,437	18,280	10,858
Total assets	4,037,077				3,667,649				4,037,077	3,667,649	3,019,052
Stockholders' equity	366,028				316,699				366,028	316,699	279,017
Retail Banking Division [Member]
Segment Reporting Information [Line Items]
Net interest income									140,460	110,582	113,347
Provision for loan losses									4,822	11,486	31,089
Noninterest income									32,337	25,282	44,885
Noninterest expense:
Salaries and employee benefits									55,101	43,524	45,456
Equipment and occupancy expenses									16,097	11,599	12,726
Data processing and telecommunications expenses									14,436	10,957	10,341
Other expenses									39,175	36,850	41,056
Total noninterest expense									124,809	102,930	109,579
Income before income tax expense									43,166	21,448	17,564
Income tax expense									12,918	6,536	5,831
Net income									30,248	14,912	11,733
Less preferred stock dividends									286	1,738	3,577
Net income available to common shareholders									29,962	13,174	8,156
Total assets	3,751,503				3,506,954				3,751,503	3,506,954	2,938,519
Stockholders' equity	353,532				312,678				353,532	312,678	278,901
Mortgage Banking Division [Member]
Segment Reporting Information [Line Items]
Net interest income									7,360	3,883	1,058
Provision for loan losses									826
Noninterest income									25,614	19,130	12,989
Noninterest expense:
Salaries and employee benefits									16,173	12,515	7,666
Equipment and occupancy expenses									1,343	631	482
Data processing and telecommunications expenses									1,097	573	342
Other expenses									3,995	4,386	1,401
Total noninterest expense									22,608	18,105	9,891
Income before income tax expense									9,540	4,908	4,156
Income tax expense									3,339	1,718	1,454
Net income									6,201	3,190	2,702
Net income available to common shareholders									6,201	3,190	2,702
Total assets	223,090				122,427				223,090	122,427	80,533
Stockholders' equity	8,306				2,105				8,306	2,105	116
SBA Division [Member]
Segment Reporting Information [Line Items]
Net interest income									2,066	1,720
Noninterest income									4,885	2,137
Noninterest expense:
Salaries and employee benefits									2,604	631
Equipment and occupancy expenses									81	56
Data processing and telecommunications expenses									18	9
Other expenses									749	214
Total noninterest expense									3,452	910
Income before income tax expense									3,499	2,947
Income tax expense									1,225	1,031
Net income									2,274	1,916
Net income available to common shareholders									2,274	1,916
Total assets	62,484				38,268				62,484	38,268
Stockholders' equity	$ 4,190				$ 1,916				$ 4,190	$ 1,916