SEGMENT REPORTING - Schedule of Segment Reporting, by Reportable Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Interest income	$ 173,751	$ 185,018	$ 351,701	$ 367,786
Interest expense	11,899	21,204	24,872	56,027
Net interest income	161,852	163,814	326,829	311,759
Provision for credit losses	142	88,161	(28,449)	129,208
Noninterest income	89,240	120,960	207,213	175,339
Noninterest expense
Salaries and employee benefits	85,505	95,168	181,490	171,114
Occupancy and equipment	10,812	13,807	22,593	25,835
Data processing and communications expenses	11,877	10,514	23,761	22,468
Other expenses	27,567	36,279	56,715	74,404
Total noninterest expense	135,761	155,768	284,559	293,821
Income (loss) before income tax expense	115,189	40,845	277,932	64,069
Income tax expense (benefit)	26,862	8,609	64,643	12,511
Net income (loss)	88,327	32,236	213,289	51,558
Total assets	21,886,931	19,872,629	21,886,931	19,872,629	$ 20,438,638
Goodwill	928,005	928,005	928,005	928,005	928,005
Other intangible assets, net	63,783	80,354	63,783	80,354	$ 71,974
Banking Division
Segment Reporting Information [Line Items]
Interest income	109,260	128,653	221,639	260,954
Interest expense	(1,410)	8,323	(1,847)	22,249
Net interest income	110,670	120,330	223,486	238,705
Provision for credit losses	(3,949)	86,805	(27,853)	122,802
Noninterest income	16,171	14,468	32,909	32,241
Noninterest expense
Salaries and employee benefits	37,814	40,423	80,537	82,044
Occupancy and equipment	9,050	11,679	19,170	22,026
Data processing and communications expenses	10,280	8,919	20,481	19,716
Other expenses	18,763	27,997	38,473	58,642
Total noninterest expense	75,907	89,018	158,661	182,428
Income (loss) before income tax expense	54,883	(41,025)	125,587	(34,284)
Income tax expense (benefit)	14,196	(8,582)	32,652	(8,307)
Net income (loss)	40,687	(32,443)	92,935	(25,977)
Total assets	15,561,628	13,121,679	15,561,628	13,121,679
Goodwill	863,507	863,507	863,507	863,507
Other intangible assets, net	50,418	64,007	50,418	64,007
Retail Mortgage Division
Segment Reporting Information [Line Items]
Interest income	34,085	34,714	64,284	68,125
Interest expense	11,552	10,412	22,767	26,067
Net interest income	22,533	24,302	41,517	42,058
Provision for credit losses	5,647	423	1,094	2,420
Noninterest income	69,055	104,195	166,695	138,564
Noninterest expense
Salaries and employee benefits	44,798	50,003	94,636	81,100
Occupancy and equipment	1,553	1,953	3,029	3,457
Data processing and communications expenses	1,435	1,406	2,981	2,392
Other expenses	7,638	6,949	15,827	12,824
Total noninterest expense	55,424	60,311	116,473	99,773
Income (loss) before income tax expense	30,517	67,763	90,645	78,429
Income tax expense (benefit)	6,408	14,231	19,035	16,639
Net income (loss)	24,109	53,532	71,610	61,790
Total assets	3,917,275	3,905,683	3,917,275	3,905,683
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Warehouse Lending Division
Segment Reporting Information [Line Items]
Interest income	8,988	5,285	19,315	10,135
Interest expense	268	259	689	1,807
Net interest income	8,720	5,026	18,626	8,328
Provision for credit losses	(155)	403	(300)	394
Noninterest income	1,333	727	2,313	1,687
Noninterest expense
Salaries and employee benefits	278	209	608	419
Occupancy and equipment	1	1	2	2
Data processing and communications expenses	68	55	117	96
Other expenses	30	88	63	122
Total noninterest expense	377	353	790	639
Income (loss) before income tax expense	9,831	4,997	20,449	8,982
Income tax expense (benefit)	2,064	1,049	4,294	1,886
Net income (loss)	7,767	3,948	16,155	7,096
Total assets	779,234	753,668	779,234	753,668
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
SBA Division
Segment Reporting Information [Line Items]
Interest income	14,050	8,757	32,084	12,485
Interest expense	1,168	1,723	2,567	3,270
Net interest income	12,882	7,034	29,517	9,215
Provision for credit losses	(607)	2,322	(1,154)	1,419
Noninterest income	2,677	1,570	5,288	2,847
Noninterest expense
Salaries and employee benefits	937	2,612	2,319	4,088
Occupancy and equipment	132	97	238	194
Data processing and communications expenses	0	15	1	28
Other expenses	284	359	579	874
Total noninterest expense	1,353	3,083	3,137	5,184
Income (loss) before income tax expense	14,813	3,199	32,822	5,459
Income tax expense (benefit)	3,111	671	6,893	1,146
Net income (loss)	11,702	2,528	25,929	4,313
Total assets	748,234	1,310,077	748,234	1,310,077
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Premium  Finance  Division
Segment Reporting Information [Line Items]
Interest income	7,368	7,609	14,379	16,087
Interest expense	321	487	696	2,634
Net interest income	7,047	7,122	13,683	13,453
Provision for credit losses	(794)	(1,792)	(236)	2,173
Noninterest income	4	0	8	0
Noninterest expense
Salaries and employee benefits	1,678	1,921	3,390	3,463
Occupancy and equipment	76	77	154	156
Data processing and communications expenses	94	119	181	236
Other expenses	852	886	1,773	1,942
Total noninterest expense	2,700	3,003	5,498	5,797
Income (loss) before income tax expense	5,145	5,911	8,429	5,483
Income tax expense (benefit)	1,083	1,240	1,769	1,147
Net income (loss)	4,062	4,671	6,660	4,336
Total assets	880,560	781,522	880,560	781,522
Goodwill	64,498	64,498	64,498	64,498
Other intangible assets, net	$ 13,365	$ 16,347	$ 13,365	$ 16,347