SEGMENT REPORTING - Schedule of Segment Reporting, by Reportable Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Interest income	$ 182,768	$ 124,929
Interest expense	34,823	25,534
Net interest income	147,945	99,395
Provision for credit losses	41,047	3,408
Noninterest income	54,379	30,771
Noninterest expense
Salaries and employee benefits	75,946	38,332
Equipment and occupancy expenses	12,028	8,204
Data processing and telecommunications expenses	11,954	8,391
Other expenses	38,125	20,498
Total noninterest expense	138,053	75,425
Income before income tax expense	23,224	51,333
Income tax expense (benefit)	3,902	11,428
Net income	19,322	39,905
Total assets	18,224,548	11,656,275	$ 18,242,579
Goodwill	931,947	501,308	931,637
Other intangible assets, net	85,955	55,557	$ 91,586
Banking Division
Segment Reporting Information [Line Items]
Interest income	132,301	97,874
Interest expense	13,926	12,835
Net interest income	118,375	85,039
Provision for credit losses	35,997	2,058
Noninterest income	17,773	14,370
Noninterest expense
Salaries and employee benefits	41,621	27,932
Equipment and occupancy expenses	10,347	7,281
Data processing and telecommunications expenses	10,797	7,592
Other expenses	30,645	16,956
Total noninterest expense	93,410	59,761
Income before income tax expense	6,741	37,590
Income tax expense (benefit)	275	8,775
Net income	6,466	28,815
Total assets	13,201,373	9,457,529
Goodwill	867,449	436,810
Other intangible assets, net	68,857	35,455
Retail Mortgage Division
Segment Reporting Information [Line Items]
Interest income	33,411	12,512
Interest expense	15,655	6,759
Net interest income	17,756	5,753
Provision for credit losses	1,997	136
Noninterest income	34,369	14,290
Noninterest expense
Salaries and employee benefits	31,097	8,207
Equipment and occupancy expenses	1,504	766
Data processing and telecommunications expenses	986	330
Other expenses	5,875	2,114
Total noninterest expense	39,462	11,417
Income before income tax expense	10,666	8,490
Income tax expense (benefit)	2,408	1,613
Net income	8,258	6,877
Total assets	3,466,766	1,184,097
Goodwill	0	0
Other intangible assets, net	0	0
Warehouse Lending Division
Segment Reporting Information [Line Items]
Interest income	4,850	4,804
Interest expense	1,548	2,114
Net interest income	3,302	2,690
Provision for credit losses	(9)	0
Noninterest income	960	379
Noninterest expense
Salaries and employee benefits	210	161
Equipment and occupancy expenses	1	1
Data processing and telecommunications expenses	41	30
Other expenses	34	68
Total noninterest expense	286	260
Income before income tax expense	3,985	2,809
Income tax expense (benefit)	837	590
Net income	3,148	2,219
Total assets	548,837	296,357
Goodwill	0	0
Other intangible assets, net	0	0
SBA Division
Segment Reporting Information [Line Items]
Interest income	3,728	2,174
Interest expense	1,547	1,088
Net interest income	2,181	1,086
Provision for credit losses	(903)	231
Noninterest income	1,277	1,730
Noninterest expense
Salaries and employee benefits	1,476	727
Equipment and occupancy expenses	97	59
Data processing and telecommunications expenses	13	2
Other expenses	515	387
Total noninterest expense	2,101	1,175
Income before income tax expense	2,260	1,410
Income tax expense (benefit)	475	296
Net income	1,785	1,114
Total assets	252,668	142,769
Goodwill	0	0
Other intangible assets, net	0	0
Premium  Finance  Division
Segment Reporting Information [Line Items]
Interest income	8,478	7,565
Interest expense	2,147	2,738
Net interest income	6,331	4,827
Provision for credit losses	3,965	983
Noninterest income	0	2
Noninterest expense
Salaries and employee benefits	1,542	1,305
Equipment and occupancy expenses	79	97
Data processing and telecommunications expenses	117	437
Other expenses	1,056	973
Total noninterest expense	2,794	2,812
Income before income tax expense	(428)	1,034
Income tax expense (benefit)	(93)	154
Net income	(335)	880
Total assets	754,904	575,523
Goodwill	64,498	64,498
Other intangible assets, net	$ 17,098	$ 20,102