SEGMENT REPORTING - Schedule of Segment Reporting, by Reportable Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Interest income	$ 177,950	$ 182,768
Interest expense	12,973	34,823
Net interest income	164,977	147,945
Provision for credit losses	(28,591)	41,047
Noninterest income	117,973	54,379
Noninterest expense
Salaries and employee benefits	95,985	75,946
Equipment and occupancy expenses	11,781	12,028
Data processing and telecommunications expenses	11,884	11,954
Other expenses	29,148	38,125
Total noninterest expense	148,798	138,053
Income (loss) before income tax expense	162,743	23,224
Income tax expense (benefit)	37,781	3,902
Net income (loss)	124,962	19,322
Total assets	21,427,127	18,224,548	$ 20,438,638
Goodwill	928,005	931,947	928,005
Other intangible assets, net	67,848	85,955	$ 71,974
Banking Division
Segment Reporting Information [Line Items]
Interest income	112,379	132,301
Interest expense	(437)	13,926
Net interest income	112,816	118,375
Provision for credit losses	(23,904)	35,997
Noninterest income	16,738	17,773
Noninterest expense
Salaries and employee benefits	42,723	41,621
Equipment and occupancy expenses	10,120	10,347
Data processing and telecommunications expenses	10,201	10,797
Other expenses	19,710	30,645
Total noninterest expense	82,754	93,410
Income (loss) before income tax expense	70,704	6,741
Income tax expense (benefit)	18,456	275
Net income (loss)	52,248	6,466
Total assets	14,591,933	13,201,373
Goodwill	863,507	867,449
Other intangible assets, net	53,745	68,857
Retail Mortgage Division
Segment Reporting Information [Line Items]
Interest income	30,199	33,411
Interest expense	11,215	15,655
Net interest income	18,984	17,756
Provision for credit losses	(4,553)	1,997
Noninterest income	97,640	34,369
Noninterest expense
Salaries and employee benefits	49,838	31,097
Equipment and occupancy expenses	1,476	1,504
Data processing and telecommunications expenses	1,546	986
Other expenses	8,189	5,875
Total noninterest expense	61,049	39,462
Income (loss) before income tax expense	60,128	10,666
Income tax expense (benefit)	12,627	2,408
Net income (loss)	47,501	8,258
Total assets	4,086,210	3,466,766
Goodwill	0	0
Other intangible assets, net	0	0
Warehouse Lending Division
Segment Reporting Information [Line Items]
Interest income	10,327	4,850
Interest expense	421	1,548
Net interest income	9,906	3,302
Provision for credit losses	(145)	(9)
Noninterest income	980	960
Noninterest expense
Salaries and employee benefits	330	210
Equipment and occupancy expenses	1	1
Data processing and telecommunications expenses	49	41
Other expenses	33	34
Total noninterest expense	413	286
Income (loss) before income tax expense	10,618	3,985
Income tax expense (benefit)	2,230	837
Net income (loss)	8,388	3,148
Total assets	886,004	548,837
Goodwill	0	0
Other intangible assets, net	0	0
SBA Division
Segment Reporting Information [Line Items]
Interest income	18,034	3,728
Interest expense	1,399	1,547
Net interest income	16,635	2,181
Provision for credit losses	(547)	(903)
Noninterest income	2,611	1,277
Noninterest expense
Salaries and employee benefits	1,382	1,476
Equipment and occupancy expenses	106	97
Data processing and telecommunications expenses	1	13
Other expenses	295	515
Total noninterest expense	1,784	2,101
Income (loss) before income tax expense	18,009	2,260
Income tax expense (benefit)	3,782	475
Net income (loss)	14,227	1,785
Total assets	1,055,068	252,668
Goodwill	0	0
Other intangible assets, net	0	0
Premium  Finance  Division
Segment Reporting Information [Line Items]
Interest income	7,011	8,478
Interest expense	375	2,147
Net interest income	6,636	6,331
Provision for credit losses	558	3,965
Noninterest income	4	0
Noninterest expense
Salaries and employee benefits	1,712	1,542
Equipment and occupancy expenses	78	79
Data processing and telecommunications expenses	87	117
Other expenses	921	1,056
Total noninterest expense	2,798	2,794
Income (loss) before income tax expense	3,284	(428)
Income tax expense (benefit)	686	(93)
Net income (loss)	2,598	(335)
Total assets	807,912	754,904
Goodwill	64,498	64,498
Other intangible assets, net	$ 14,103	$ 17,098