SEGMENT REPORTING - Schedule of Segment Reporting, by Reportable Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Interest income	$ 185,018	$ 129,028	$ 367,786	$ 253,957
Interest expense	21,204	27,377	56,027	52,911
Net interest income	163,814	101,651	311,759	201,046
Provision for credit losses	88,161	4,668	129,208	8,076
Noninterest income	120,960	35,236	175,339	66,007
Noninterest expense
Salaries and employee benefits	95,168	38,331	171,114	76,663
Equipment and occupancy expenses	13,807	7,834	25,835	16,038
Data processing and telecommunications expenses	10,514	8,388	22,468	16,779
Other expenses	36,279	26,698	74,404	47,196
Total noninterest expense	155,768	81,251	293,821	156,676
Income before income tax expense	40,845	50,968	64,069	102,301
Income tax expense	8,609	12,064	12,511	23,492
Net income	32,236	38,904	51,558	78,809
Total assets	19,872,629	11,889,336	19,872,629	11,889,336	$ 18,242,579
Goodwill	928,005	501,140	928,005	501,140	931,637
Other intangible assets, net	80,354	52,437	80,354	52,437	91,586
Banking Division
Segment Reporting Information [Line Items]
Interest income	128,653	98,892	260,954	196,766
Interest expense	8,323	14,137	22,249	26,972
Net interest income	120,330	84,755	238,705	169,794
Provision for credit losses	86,805	2,306	122,802	4,364
Noninterest income	14,468	14,830	32,241	29,200
Noninterest expense
Salaries and employee benefits	40,423	24,228	82,044	52,160
Equipment and occupancy expenses	11,679	7,034	22,026	14,315
Data processing and telecommunications expenses	8,919	7,635	19,716	15,227
Other expenses	27,997	22,728	58,642	39,684
Total noninterest expense	89,018	61,625	182,428	121,386
Income before income tax expense	(41,025)	35,654	(34,284)	73,244
Income tax expense	(8,582)	8,691	(8,307)	17,466
Net income	(32,443)	26,963	(25,977)	55,778
Total assets	13,121,679	9,208,685	13,121,679	9,208,685
Goodwill	863,507	436,642	863,507	436,642	867,100
Other intangible assets, net	64,007	33,086	64,007	33,086
Retail Mortgage Division
Segment Reporting Information [Line Items]
Interest income	34,714	13,633	68,125	26,145
Interest expense	10,412	6,066	26,067	12,825
Net interest income	24,302	7,567	42,058	13,320
Provision for credit losses	423	609	2,420	745
Noninterest income	104,195	18,070	138,564	32,360
Noninterest expense
Salaries and employee benefits	50,003	11,886	81,100	20,093
Equipment and occupancy expenses	1,953	670	3,457	1,436
Data processing and telecommunications expenses	1,406	394	2,392	724
Other expenses	6,949	2,385	12,824	4,499
Total noninterest expense	60,311	15,335	99,773	26,752
Income before income tax expense	67,763	9,693	78,429	18,183
Income tax expense	14,231	2,170	16,639	3,783
Net income	53,532	7,523	61,790	14,400
Total assets	3,905,683	1,306,063	3,905,683	1,306,063
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Warehouse Lending Division
Segment Reporting Information [Line Items]
Interest income	5,285	5,550	10,135	10,354
Interest expense	259	2,563	1,807	4,677
Net interest income	5,026	2,987	8,328	5,677
Provision for credit losses	403	0	394	0
Noninterest income	727	450	1,687	829
Noninterest expense
Salaries and employee benefits	209	162	419	323
Equipment and occupancy expenses	1	1	2	2
Data processing and telecommunications expenses	55	38	96	68
Other expenses	88	75	122	143
Total noninterest expense	353	276	639	536
Income before income tax expense	4,997	3,161	8,982	5,970
Income tax expense	1,049	664	1,886	1,254
Net income	3,948	2,497	7,096	4,716
Total assets	753,668	462,780	753,668	462,780
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
SBA Division
Segment Reporting Information [Line Items]
Interest income	8,757	2,287	12,485	4,461
Interest expense	1,723	1,105	3,270	2,193
Net interest income	7,034	1,182	9,215	2,268
Provision for credit losses	2,322	178	1,419	409
Noninterest income	1,570	1,883	2,847	3,613
Noninterest expense
Salaries and employee benefits	2,612	735	4,088	1,462
Equipment and occupancy expenses	97	65	194	124
Data processing and telecommunications expenses	15	3	28	5
Other expenses	359	359	874	746
Total noninterest expense	3,083	1,162	5,184	2,337
Income before income tax expense	3,199	1,725	5,459	3,135
Income tax expense	671	362	1,146	658
Net income	2,528	1,363	4,313	2,477
Total assets	1,310,077	211,433	1,310,077	211,433
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Premium  Finance  Division
Segment Reporting Information [Line Items]
Interest income	7,609	8,666	16,087	16,231
Interest expense	487	3,506	2,634	6,244
Net interest income	7,122	5,160	13,453	9,987
Provision for credit losses	(1,792)	1,575	2,173	2,558
Noninterest income	0	3	0	5
Noninterest expense
Salaries and employee benefits	1,921	1,320	3,463	2,625
Equipment and occupancy expenses	77	64	156	161
Data processing and telecommunications expenses	119	318	236	755
Other expenses	886	1,151	1,942	2,124
Total noninterest expense	3,003	2,853	5,797	5,665
Income before income tax expense	5,911	735	5,483	1,769
Income tax expense	1,240	177	1,147	331
Net income	4,671	558	4,336	1,438
Total assets	781,522	700,375	781,522	700,375
Goodwill	64,498	64,498	64,498	64,498	$ 64,500
Other intangible assets, net	$ 16,347	$ 19,351	$ 16,347	$ 19,351