SEGMENT REPORTING - Schedule of Segment Reporting, by Reportable Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Interest income	$ 173,046	$ 179,934	$ 524,747	$ 547,720
Interest expense	11,385	17,396	36,257	73,423
Net interest income	161,661	162,538	488,490	474,297
Provision for credit losses	(9,675)	17,682	(38,124)	146,890
Noninterest income	76,562	159,018	283,775	334,357
Noninterest expense
Salaries and employee benefits	79,671	96,698	261,161	267,812
Occupancy and equipment	11,979	13,805	34,572	39,640
Data processing and communications expenses	10,681	12,226	34,442	34,694
Other expenses	34,865	30,963	91,580	105,367
Total noninterest expense	137,196	153,692	421,755	447,513
Income (loss) before income tax expense	110,702	150,182	388,634	214,251
Income tax expense (benefit)	29,022	34,037	93,665	46,548
Net income (loss)	81,680	116,145	294,969	167,703
Total assets	22,533,141	19,873,851	22,533,141	19,873,851	$ 20,438,638
Goodwill	928,005	928,005	928,005	928,005	928,005
Other intangible assets, net	60,396	76,164	60,396	76,164	$ 71,974
Banking Division
Segment Reporting Information [Line Items]
Interest income	110,708	123,593	332,347	384,547
Interest expense	(2,816)	4,031	(4,663)	26,280
Net interest income	113,524	119,562	337,010	358,267
Provision for credit losses	(9,578)	487	(37,431)	123,289
Noninterest income	17,896	15,265	50,805	47,506
Noninterest expense
Salaries and employee benefits	40,020	39,718	120,557	121,762
Occupancy and equipment	10,196	11,955	29,366	33,981
Data processing and communications expenses	9,159	9,716	29,640	29,432
Other expenses	21,723	21,517	60,196	80,159
Total noninterest expense	81,098	82,906	239,759	265,334
Income (loss) before income tax expense	59,900	51,434	185,487	17,150
Income tax expense (benefit)	17,784	13,453	50,436	5,146
Net income (loss)	42,116	37,981	135,051	12,004
Total assets	16,070,583	13,098,562	16,070,583	13,098,562
Goodwill	863,507	863,507	863,507	863,507
Other intangible assets, net	47,768	60,568	47,768	60,568
Retail Mortgage Division
Segment Reporting Information [Line Items]
Interest income	33,390	31,040	97,674	99,165
Interest expense	12,101	10,647	34,868	36,714
Net interest income	21,289	20,393	62,806	62,451
Provision for credit losses	1,678	15,051	2,772	17,471
Noninterest income	55,555	137,583	222,250	276,147
Noninterest expense
Salaries and employee benefits	36,373	53,500	131,009	134,600
Occupancy and equipment	1,590	1,676	4,619	5,133
Data processing and communications expenses	1,357	2,349	4,338	4,741
Other expenses	11,675	7,889	27,502	20,713
Total noninterest expense	50,995	65,414	167,468	165,187
Income (loss) before income tax expense	24,171	77,511	114,816	155,940
Income tax expense (benefit)	5,076	16,112	24,111	32,751
Net income (loss)	19,095	61,399	90,705	123,189
Total assets	4,247,967	3,632,999	4,247,967	3,632,999
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Warehouse Lending Division
Segment Reporting Information [Line Items]
Interest income	9,093	6,844	28,408	16,979
Interest expense	381	298	1,070	2,105
Net interest income	8,712	6,546	27,338	14,874
Provision for credit losses	(291)	495	(591)	889
Noninterest income	1,037	1,064	3,350	2,751
Noninterest expense
Salaries and employee benefits	264	266	872	685
Occupancy and equipment	0	1	2	3
Data processing and communications expenses	59	73	176	169
Other expenses	200	28	263	150
Total noninterest expense	523	368	1,313	1,007
Income (loss) before income tax expense	9,517	6,747	29,966	15,729
Income tax expense (benefit)	1,999	1,431	6,293	3,317
Net income (loss)	7,518	5,316	23,673	12,412
Total assets	740,809	1,002,027	740,809	1,002,027
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
SBA Division
Segment Reporting Information [Line Items]
Interest income	11,986	10,958	44,070	23,443
Interest expense	1,287	1,992	3,854	5,262
Net interest income	10,699	8,966	40,216	18,181
Provision for credit losses	(1,104)	4,297	(2,258)	5,716
Noninterest income	2,070	5,106	7,358	7,953
Noninterest expense
Salaries and employee benefits	1,320	1,572	3,639	5,660
Occupancy and equipment	116	97	354	291
Data processing and communications expenses	18	4	19	32
Other expenses	370	595	949	1,469
Total noninterest expense	1,824	2,268	4,961	7,452
Income (loss) before income tax expense	12,049	7,507	44,871	12,966
Income tax expense (benefit)	2,530	1,577	9,423	2,723
Net income (loss)	9,519	5,930	35,448	10,243
Total assets	529,044	1,338,794	529,044	1,338,794
Goodwill	0	0	0	0
Other intangible assets, net	0	0	0	0
Premium  Finance  Division
Segment Reporting Information [Line Items]
Interest income	7,869	7,499	22,248	23,586
Interest expense	432	428	1,128	3,062
Net interest income	7,437	7,071	21,120	20,524
Provision for credit losses	(380)	(2,648)	(616)	(475)
Noninterest income	4	0	12	0
Noninterest expense
Salaries and employee benefits	1,694	1,642	5,084	5,105
Occupancy and equipment	77	76	231	232
Data processing and communications expenses	88	84	269	320
Other expenses	897	934	2,670	2,876
Total noninterest expense	2,756	2,736	8,254	8,533
Income (loss) before income tax expense	5,065	6,983	13,494	12,466
Income tax expense (benefit)	1,633	1,464	3,402	2,611
Net income (loss)	3,432	5,519	10,092	9,855
Total assets	944,738	801,469	944,738	801,469
Goodwill	64,498	64,498	64,498	64,498
Other intangible assets, net	$ 12,628	$ 15,596	$ 12,628	$ 15,596