SEGMENT REPORTING - Schedule of Segment Reporting, by Reportable Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Interest income	$ 89,946	$ 71,411	$ 169,458	$ 138,461
Interest expense	13,947	8,254	24,658	14,714
Net interest income	75,999	63,157	144,800	123,747
Provision for loan losses	9,110	2,205	10,911	4,041	$ 8,364
Noninterest income	31,307	28,189	57,771	53,895
Noninterest expense
Salaries and employee benefits	39,776	29,132	71,865	56,926
Equipment and occupancy expenses	6,390	6,146	12,588	12,023
Data processing and telecommunications expenses	6,439	7,028	13,574	13,600
Other expenses	33,781	13,433	47,457	26,283
Total noninterest expense	86,386	55,739	145,484	108,832
Income before income tax expense	11,810	33,402	46,176	64,769
Income tax expense	2,423	10,315	10,129	20,529
Net income	9,387	23,087	36,047	44,240
Total assets	11,190,697	7,397,858	11,190,697	7,397,858	7,856,203
Goodwill	504,764	125,532	504,764	125,532	125,532
Other intangible assets, net	53,561	15,378	53,561	15,378	$ 13,496
Banking Division
Segment Reporting Information [Line Items]
Interest income	68,398	56,694	129,294	110,906
Interest expense	6,639	4,894	12,176	8,980
Net interest income	61,759	51,800	117,118	101,926
Provision for loan losses	766	1,491	1,654	3,473
Noninterest income	13,287	12,954	26,386	25,967
Noninterest expense
Salaries and employee benefits	26,646	19,359	48,714	38,203
Equipment and occupancy expenses	5,684	5,427	11,161	10,684
Data processing and telecommunications expenses	5,611	6,378	11,915	12,421
Other expenses	29,937	10,209	41,017	19,450
Total noninterest expense	67,878	41,373	112,807	80,758
Income before income tax expense	6,402	21,890	29,043	43,662
Income tax expense	1,716	6,095	6,958	12,951
Net income	4,686	15,795	22,085	30,711
Total assets	9,380,969	6,186,980	9,380,969	6,186,980
Goodwill	437,605	125,532	437,605	125,532
Other intangible assets, net	33,507	15,378	33,507	15,378
Retail Mortgage Division
Segment Reporting Information [Line Items]
Interest income	7,973	4,974	14,795	9,028
Interest expense	2,927	1,504	4,752	2,582
Net interest income	5,046	3,470	10,043	6,446
Provision for loan losses	246	347	463	355
Noninterest income	13,889	13,053	25,474	23,566
Noninterest expense
Salaries and employee benefits	10,864	7,763	18,606	14,979
Equipment and occupancy expenses	545	610	1,138	1,129
Data processing and telecommunications expenses	383	440	772	757
Other expenses	1,778	888	3,509	2,029
Total noninterest expense	13,570	9,701	24,025	18,894
Income before income tax expense	5,119	6,475	11,029	10,763
Income tax expense	1,075	2,361	2,319	3,862
Net income	4,044	4,114	8,710	6,901
Total assets	727,639	475,599	727,639	475,599
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Warehouse Lending Division
Segment Reporting Information [Line Items]
Interest income	3,641	1,613	6,393	2,946
Interest expense	1,315	359	2,212	587
Net interest income	2,326	1,254	4,181	2,359
Provision for loan losses	0	176	0	(56)
Noninterest income	735	438	1,132	757
Noninterest expense
Salaries and employee benefits	128	127	266	274
Equipment and occupancy expenses	0	1	0	2
Data processing and telecommunications expenses	30	25	63	52
Other expenses	55	54	107	86
Total noninterest expense	213	207	436	414
Income before income tax expense	2,848	1,309	4,877	2,758
Income tax expense	598	472	1,024	979
Net income	2,250	837	3,853	1,779
Total assets	324,706	174,149	324,706	174,149
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
SBA Division
Segment Reporting Information [Line Items]
Interest income	1,907	1,258	3,338	2,471
Interest expense	587	373	1,094	679
Net interest income	1,320	885	2,244	1,792
Provision for loan losses	447	51	984	99
Noninterest income	1,349	1,718	2,719	3,533
Noninterest expense
Salaries and employee benefits	736	890	1,476	1,481
Equipment and occupancy expenses	55	54	113	105
Data processing and telecommunications expenses	9	2	18	3
Other expenses	290	259	526	470
Total noninterest expense	1,090	1,205	2,133	2,059
Income before income tax expense	1,132	1,347	1,846	3,167
Income tax expense	238	472	388	1,109
Net income	894	875	1,458	2,058
Total assets	142,116	80,909	142,116	80,909
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Premium Finance Division
Segment Reporting Information [Line Items]
Interest income	8,027	6,872	15,638	13,110
Interest expense	2,479	1,124	4,424	1,886
Net interest income	5,548	5,748	11,214	11,224
Provision for loan losses	7,651	140	7,810	170
Noninterest income	2,047	26	2,060	72
Noninterest expense
Salaries and employee benefits	1,402	993	2,803	1,989
Equipment and occupancy expenses	106	54	176	103
Data processing and telecommunications expenses	406	183	806	367
Other expenses	1,721	2,023	2,298	4,248
Total noninterest expense	3,635	3,253	6,083	6,707
Income before income tax expense	(3,691)	2,381	(619)	4,419
Income tax expense	(1,204)	915	(560)	1,628
Net income	(2,487)	1,466	(59)	2,791
Total assets	615,267	480,221	615,267	480,221
Goodwill	67,159	0	67,159	0
Other intangible assets, net	$ 20,054	$ 0	$ 20,054	$ 0