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
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net interest income	$ 38,832	$ 34,484
Provision for loan losses	1,069	1,726	5,648
Noninterest income	17,575	12,754
Noninterest expense:
Salaries and employee benefits	20,632	17,394
Equipment and occupancy expenses	4,554	4,064
Data processing and telecommunications expenses	4,260	3,454
Other expenses	11,381	8,327
Total noninterest expense	40,827	33,239
Income before income tax expense	14,511	12,273
Income tax expense	4,747	3,923
Net income	9,764	8,350
Less preferred stock dividends		286
Net income available to common shareholders	9,764	8,064
Total assets	4,152,904	3,487,984	4,037,077
Intangible assets	71,138	40,526
Retail Banking Division [Member]
Segment Reporting Information [Line Items]
Net interest income	35,839	32,928
Provision for loan losses	927	1,726
Noninterest income	8,780	7,361
Noninterest expense:
Salaries and employee benefits	15,362	13,577
Equipment and occupancy expenses	4,144	3,749
Data processing and telecommunications expenses	4,011	3,326
Other expenses	10,356	7,380
Total noninterest expense	33,873	28,032
Income before income tax expense	9,819	10,531
Income tax expense	3,105	3,313
Net income	6,714	7,218
Less preferred stock dividends		286
Net income available to common shareholders	6,714	6,932
Total assets	3,839,417	3,315,731
Intangible assets	71,138	40,526
Mortgage Banking Division [Member]
Segment Reporting Information [Line Items]
Net interest income	2,380	1,100
Provision for loan losses	142
Noninterest income	7,883	5,164
Noninterest expense:
Salaries and employee benefits	4,654	3,568
Equipment and occupancy expenses	382	302
Data processing and telecommunications expenses	245	122
Other expenses	968	815
Total noninterest expense	6,249	4,807
Income before income tax expense	3,872	1,457
Income tax expense	1,355	510
Net income	2,517	947
Net income available to common shareholders	2,517	947
Total assets	244,477	128,072
SBA Division [Member]
Segment Reporting Information [Line Items]
Net interest income	613	456
Noninterest income	912	229
Noninterest expense:
Salaries and employee benefits	616	249
Equipment and occupancy expenses	28	13
Data processing and telecommunications expenses	4	6
Other expenses	57	132
Total noninterest expense	705	400
Income before income tax expense	820	285
Income tax expense	287	100
Net income	533	185
Net income available to common shareholders	533	185
Total assets	$ 69,010	$ 44,181