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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Interest income	$ 129,028	$ 89,946	$ 253,957	$ 169,458
Interest expense	27,377	13,947	52,911	24,658
Net interest income	101,651	75,999	201,046	144,800
Provision for loan losses	4,668	9,110	8,076	10,911	$ 16,667
Noninterest income	35,236	31,307	66,007	57,771
Noninterest expense
Salaries and employee benefits	38,441	39,776	76,811	71,865
Equipment and occupancy expenses	7,834	6,390	16,038	12,588
Data processing and telecommunications expenses	8,388	6,439	16,779	13,574
Other expenses	26,588	33,781	47,048	47,457
Total noninterest expense	81,251	86,386	156,676	145,484
Income before income tax expense	50,968	11,810	102,301	46,176
Income tax expense	12,064	2,423	23,492	10,129
Net income	38,904	9,387	78,809	36,047
Total assets	11,889,336	11,190,697	11,889,336	11,190,697	11,443,515
Goodwill	501,140	504,764	501,140	504,764	503,434
Other intangible assets, net	52,437	53,561	52,437	53,561	$ 58,689
Banking Division
Segment Reporting Information [Line Items]
Interest income	98,892	68,398	196,766	129,294
Interest expense	14,137	6,639	26,972	12,176
Net interest income	84,755	61,759	169,794	117,118
Provision for loan losses	2,306	766	4,364	1,654
Noninterest income	14,830	13,287	29,200	26,386
Noninterest expense
Salaries and employee benefits	24,228	26,646	52,160	48,714
Equipment and occupancy expenses	7,034	5,684	14,315	11,161
Data processing and telecommunications expenses	7,635	5,611	15,227	11,915
Other expenses	22,728	29,937	39,684	41,017
Total noninterest expense	61,625	67,878	121,386	112,807
Income before income tax expense	35,654	6,402	73,244	29,043
Income tax expense	8,691	1,716	17,466	6,958
Net income	26,963	4,686	55,778	22,085
Total assets	9,208,685	9,380,969	9,208,685	9,380,969
Goodwill	436,642	437,605	436,642	437,605
Other intangible assets, net	33,086	33,507	33,086	33,507
Retail Mortgage Division
Segment Reporting Information [Line Items]
Interest income	13,633	7,973	26,145	14,795
Interest expense	6,066	2,927	12,825	4,752
Net interest income	7,567	5,046	13,320	10,043
Provision for loan losses	609	246	745	463
Noninterest income	18,070	13,889	32,360	25,474
Noninterest expense
Salaries and employee benefits	11,886	10,864	20,093	18,606
Equipment and occupancy expenses	670	545	1,436	1,138
Data processing and telecommunications expenses	394	383	724	772
Other expenses	2,385	1,778	4,499	3,509
Total noninterest expense	15,335	13,570	26,752	24,025
Income before income tax expense	9,693	5,119	18,183	11,029
Income tax expense	2,170	1,075	3,783	2,319
Net income	7,523	4,044	14,400	8,710
Total assets	1,306,063	727,639	1,306,063	727,639
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Warehouse Lending Division
Segment Reporting Information [Line Items]
Interest income	5,550	3,641	10,354	6,393
Interest expense	2,563	1,315	4,677	2,212
Net interest income	2,987	2,326	5,677	4,181
Provision for loan losses	0	0	0	0
Noninterest income	450	735	829	1,132
Noninterest expense
Salaries and employee benefits	162	128	323	266
Equipment and occupancy expenses	1	0	2	0
Data processing and telecommunications expenses	38	30	68	63
Other expenses	75	55	143	107
Total noninterest expense	276	213	536	436
Income before income tax expense	3,161	2,848	5,970	4,877
Income tax expense	664	598	1,254	1,024
Net income	2,497	2,250	4,716	3,853
Total assets	462,780	324,706	462,780	324,706
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
SBA Division
Segment Reporting Information [Line Items]
Interest income	2,287	1,907	4,461	3,338
Interest expense	1,105	587	2,193	1,094
Net interest income	1,182	1,320	2,268	2,244
Provision for loan losses	178	447	409	984
Noninterest income	1,883	1,349	3,613	2,719
Noninterest expense
Salaries and employee benefits	845	736	1,610	1,476
Equipment and occupancy expenses	65	55	124	113
Data processing and telecommunications expenses	3	9	5	18
Other expenses	249	290	598	526
Total noninterest expense	1,162	1,090	2,337	2,133
Income before income tax expense	1,725	1,132	3,135	1,846
Income tax expense	362	238	658	388
Net income	1,363	894	2,477	1,458
Total assets	211,433	142,116	211,433	142,116
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Premium Finance Division
Segment Reporting Information [Line Items]
Interest income	8,666	8,027	16,231	15,638
Interest expense	3,506	2,479	6,244	4,424
Net interest income	5,160	5,548	9,987	11,214
Provision for loan losses	1,575	7,651	2,558	7,810
Noninterest income	3	2,047	5	2,060
Noninterest expense
Salaries and employee benefits	1,320	1,402	2,625	2,803
Equipment and occupancy expenses	64	106	161	176
Data processing and telecommunications expenses	318	406	755	806
Other expenses	1,151	1,721	2,124	2,298
Total noninterest expense	2,853	3,635	5,665	6,083
Income before income tax expense	735	(3,691)	1,769	(619)
Income tax expense	177	(1,204)	331	(560)
Net income	558	(2,487)	1,438	(59)
Total assets	700,375	615,267	700,375	615,267
Goodwill	64,498	67,159	64,498	67,159
Other intangible assets, net	$ 19,351	$ 20,054	$ 19,351	$ 20,054