SEGMENT REPORTING - Schedule of Financial Information with Respect to Company's Reportable Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Interest income	$ 79,564	$ 76,322	$ 71,411	$ 67,050	$ 62,956	$ 62,210	$ 59,340	$ 54,559	$ 294,347	$ 239,065	$ 190,393
Interest expense	10,041	9,467	8,254	6,460	5,677	5,143	4,751	4,123	34,222	19,694	14,856
Net interest income	69,523	66,855	63,157	60,590	57,279	57,067	54,589	50,436	260,125	219,371	175,537
Provision for loan losses	2,536	1,787	2,205	1,836	1,710	811	889	681	8,364	4,091	5,264
Noninterest income	23,563	26,999	28,189	25,706	24,272	28,864	28,379	24,286	104,457	105,801	85,586
Noninterest expense
Salaries and employee benefits									120,016	106,837	94,003
Occupancy and equipment expenses									24,069	24,397	21,195
Data processing and communications expenses									27,869	24,591	19,849
Other expenses									59,982	60,010	64,068
Total noninterest expense	58,916	63,675	55,739	52,691	54,660	53,199	52,359	49,241	231,936	215,835	199,115
Income before income tax expense	31,213	28,300	33,402	31,367	25,164	31,921	29,720	18,441	124,282	105,246	56,744
Income tax expense	22,063	8,142	10,315	10,214	6,987	10,364	9,671	6,124	50,734	33,146	15,897
Net income	9,150	$ 20,158	$ 23,087	$ 21,153	18,177	$ 21,557	$ 20,049	$ 12,317	73,548	72,100	40,847
Total assets	7,856,203				6,892,031				7,856,203	6,892,031	5,588,940
Goodwill	125,532				125,532				125,532	125,532	90,082
Other intangible assets, net	13,496				17,428				13,496	17,428	17,058
Banking Division
Segment Reporting Information [Line Items]
Interest income									231,111	213,246	174,162
Interest expense									20,392	14,762	12,742
Net interest income									210,719	198,484	161,420
Provision for loan losses									6,787	1,973	4,847
Noninterest income									51,416	53,168	44,251
Noninterest expense
Salaries and employee benefits									78,857	72,824	68,183
Occupancy and equipment expenses									21,436	22,209	19,320
Data processing and communications expenses									25,177	23,140	18,681
Other expenses									46,192	54,438	59,636
Total noninterest expense									171,662	172,611	165,820
Income before income tax expense									83,686	77,068	35,004
Income tax expense									36,518	23,283	8,257
Net income									47,168	53,785	26,747
Total assets	6,431,151				5,879,859				6,431,151	5,879,859	5,166,045
Goodwill	125,532				125,532				125,532	125,532	90,082
Other intangible assets, net	13,496				17,428				13,496	17,428	17,058
Retail Mortgage Division
Segment Reporting Information [Line Items]
Interest income									21,318	14,110	8,821
Interest expense									5,731	3,469	1,484
Net interest income									15,587	10,641	7,337
Provision for loan losses									771	573	417
Noninterest income									44,913	45,162	34,498
Noninterest expense
Salaries and employee benefits									32,996	30,689	22,112
Occupancy and equipment expenses									2,217	1,928	1,674
Data processing and communications expenses									1,611	1,300	1,065
Other expenses									4,260	4,485	3,787
Total noninterest expense									41,084	38,402	28,638
Income before income tax expense									18,645	16,828	12,780
Income tax expense									6,526	5,891	4,504
Net income									12,119	10,937	8,276
Total assets	598,355				358,497				598,355	358,497	246,730
Goodwill	0				0				0	0	0
Other intangible assets, net	0				0				0	0	0
Warehouse Lending Division
Segment Reporting Information [Line Items]
Interest income									7,701	6,686	4,137
Interest expense									1,824	724	159
Net interest income									5,877	5,962	3,978
Provision for loan losses									186	590	0
Noninterest income									1,739	1,790	1,364
Noninterest expense
Salaries and employee benefits									530	619	519
Occupancy and equipment expenses									4	4	7
Data processing and communications expenses									98	103	95
Other expenses									163	106	123
Total noninterest expense									795	832	744
Income before income tax expense									6,635	6,330	4,598
Income tax expense									2,322	2,215	1,609
Net income									4,313	4,115	2,989
Total assets	238,561				189,670				238,561	189,670	101,893
Goodwill	0				0				0	0	0
Other intangible assets, net	0				0				0	0	0
SBA Division
Segment Reporting Information [Line Items]
Interest income									5,293	3,959	3,273
Interest expense									1,549	739	471
Net interest income									3,744	3,220	2,802
Provision for loan losses									(111)	847	0
Noninterest income									6,277	5,681	5,473
Noninterest expense
Salaries and employee benefits									3,126	2,705	3,189
Occupancy and equipment expenses									215	254	194
Data processing and communications expenses									21	4	8
Other expenses									738	712	522
Total noninterest expense									4,100	3,675	3,913
Income before income tax expense									6,032	4,379	4,362
Income tax expense									2,111	1,533	1,527
Net income									3,921	2,846	2,835
Total assets	101,737				90,908				101,737	90,908	74,272
Goodwill	0				0				0	0	0
Other intangible assets, net	0				0				0	0	0
Premium Finance Division
Segment Reporting Information [Line Items]
Interest income									28,924	1,064	0
Interest expense									4,726	0	0
Net interest income									24,198	1,064	0
Provision for loan losses									731	108	0
Noninterest income									112	0	0
Noninterest expense
Salaries and employee benefits									4,507	0	0
Occupancy and equipment expenses									197	2	0
Data processing and communications expenses									962	44	0
Other expenses									8,629	269	0
Total noninterest expense									14,295	315	0
Income before income tax expense									9,284	641	0
Income tax expense									3,257	224	0
Net income									6,027	417	0
Total assets	486,399				373,097				486,399	373,097	0
Goodwill	0				0				0	0	0
Other intangible assets, net	$ 0				$ 0				$ 0	$ 0	$ 0