Segment Reporting - Schedule of Financial Information with Respect to Company's Reportable Business Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net interest income	$ 39,132	$ 29,320	$ 108,880	$ 87,134
Provision for loan losses	1,669	2,920	4,760	10,008
Noninterest income	17,901	12,288	46,474	35,032
Noninterest expense:
Salaries and employee benefits	20,226	14,412	54,562	41,599
Equipment and occupancy expenses	4,669	3,149	12,804	9,058
Data processing and telecommunications expenses	3,928	3,072	11,322	8,478
Other expenses	9,756	8,116	30,448	25,186
Total noninterest expense	38,579	28,749	109,136	84,321
Income before income tax expense	16,785	9,939	41,458	27,837
Income tax expense	5,122	3,262	13,315	9,197
Net income	11,663	6,677	28,143	18,640
Less preferred stock dividends		443	286	1,326
Net income available to common shareholders	11,663	6,234	27,857	17,314
Total assets	3,999,408	2,818,502	3,999,408	2,818,502	3,667,649
Stockholders' equity	353,830	290,356	353,830	290,356	316,699
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net interest income	36,785	28,089	104,094	84,372
Provision for loan losses	994	2,920	4,085	10,008
Noninterest income	10,766	7,054	27,173	20,333
Noninterest expense:
Salaries and employee benefits	15,817	10,799	42,648	32,314
Equipment and occupancy expenses	4,301	3,029	11,834	8,575
Data processing and telecommunications expenses	3,622	2,908	10,551	8,013
Other expenses	8,887	7,473	27,452	22,807
Total noninterest expense	32,627	24,209	92,485	71,709
Income before income tax expense	13,930	8,014	34,697	22,988
Income tax expense	4,123	2,588	10,949	7,500
Net income	9,807	5,426	23,748	15,488
Less preferred stock dividends		443	286	1,326
Net income available to common shareholders	9,807	4,983	23,462	14,162
Total assets	3,772,050	2,707,200	3,772,050	2,707,200
Stockholders' equity	309,904	250,863	309,904	250,863
Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net interest income	2,347	1,231	4,786	2,762
Provision for loan losses	675		675
Noninterest income	7,135	5,234	19,301	14,699
Noninterest expense:
Salaries and employee benefits	4,409	3,613	11,914	9,285
Equipment and occupancy expenses	368	120	970	483
Data processing and telecommunications expenses	306	164	771	465
Other expenses	869	643	2,996	2,379
Total noninterest expense	5,952	4,540	16,651	12,612
Income before income tax expense	2,855	1,925	6,761	4,849
Income tax expense	999	674	2,366	1,697
Net income	1,856	1,251	4,395	3,152
Net income available to common shareholders	1,856	1,251	4,395	3,152
Total assets	227,358	111,302	227,358	111,302
Stockholders' equity	$ 43,926	$ 39,493	$ 43,926	$ 39,493