LOANS AND LEASES, NET - Allowance for Loan Losses and Recorded Investment in Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Sep. 30, 2018	Dec. 31, 2017
Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 21,290		$ 13,040	$ 7,534
Provision (recovery) for loan losses	33,318	$ 18,343	42,417	19,411
Charge offs	(6,523)	(339)	(9,326)	(499)
Recoveries	587	212	2,541	632
Ending balance	48,672		48,672	27,078
Ending balance: individually evaluated for impairment					$ 141	$ 0
Ending balance: collectively evaluated for impairment					48,531	13,040
Total	21,290		13,040	7,534	48,672	13,040	$ 8,862
Loans:
Ending balance: individually evaluated for impairment					16,888	15,611
Ending balance: collectively evaluated for impairment					3,418,128	2,929,378
Total loans and leases					3,435,016	2,944,989
Financing Receivable
Loans:
Total loans and leases					2,247,853	1,846,283
Financing Receivable | Asset based lending
Allowance for Credit Losses [Roll Forward]
Beginning balance	2,065		107
Provision (recovery) for loan losses	1,365		3,528
Charge offs	0		(262)
Recoveries	69		126
Ending balance	3,499		3,499
Ending balance: individually evaluated for impairment					62	0
Ending balance: collectively evaluated for impairment					3,437	107
Total	2,065		107		3,499	107
Loans:
Ending balance: individually evaluated for impairment					5,965	1,404
Ending balance: collectively evaluated for impairment					566,245	476,513
Total loans and leases					572,210	477,917
Financing Receivable | Factoring
Allowance for Credit Losses [Roll Forward]
Beginning balance	1,062		64
Provision (recovery) for loan losses	1,799		3,022
Charge offs	(1,125)		(1,375)
Recoveries	25		50
Ending balance	1,761		1,761
Ending balance: individually evaluated for impairment					12	0
Ending balance: collectively evaluated for impairment					1,749	64
Total	1,062		64		1,761	64
Loans:
Ending balance: individually evaluated for impairment					6,034	3,331
Ending balance: collectively evaluated for impairment					281,921	280,890
Total loans and leases					287,955	284,221
Financing Receivable | Lease financing
Allowance for Credit Losses [Roll Forward]
Beginning balance	1,084		59
Provision (recovery) for loan losses	1,671		1,542
Charge offs	(1,044)		(1,462)
Recoveries	254		1,826
Ending balance	1,965		1,965
Ending balance: individually evaluated for impairment					67	0
Ending balance: collectively evaluated for impairment					1,898	59
Total	1,084		59		1,965	59
Loans:
Ending balance: individually evaluated for impairment					2,299	8,877
Ending balance: collectively evaluated for impairment					319,115	256,438
Total loans and leases					321,414	265,315
Financing Receivable | Insurance premium finance
Allowance for Credit Losses [Roll Forward]
Beginning balance	972		1,031	796
Provision (recovery) for loan losses	1,797	214	1,890	265
Charge offs	(1,877)	(339)	(2,085)	(468)
Recoveries	27	146	83	153
Ending balance	919		919	746
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					919	1,031
Total	972		1,031	796	919	1,031	725
Loans:
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					307,875	337,877
Total loans and leases					307,875	337,877
Financing Receivable | SBA/USDA
Allowance for Credit Losses [Roll Forward]
Beginning balance	253		13
Provision (recovery) for loan losses	221		461
Charge offs	0		0
Recoveries	0		0
Ending balance	474		474
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					474	13
Total	253		13		474	13
Loans:
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					77,481	59,374
Total loans and leases					77,481	59,374
Financing Receivable | Other commercial finance
Allowance for Credit Losses [Roll Forward]
Beginning balance	291		28	4
Provision (recovery) for loan losses	234	0	497	0
Charge offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	525		525	4
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					525	28
Total	291		28	4	525	28	4
Loans:
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					98,956	85,145
Total loans and leases					98,956	85,145
Financing Receivable | Commercial finance
Allowance for Credit Losses [Roll Forward]
Beginning balance	5,727		1,302	800
Provision (recovery) for loan losses	7,087	214	10,940	265
Charge offs	(4,046)	(339)	(5,184)	(468)
Recoveries	375	146	2,085	153
Ending balance	9,143		9,143	750
Ending balance: individually evaluated for impairment					141	0
Ending balance: collectively evaluated for impairment					9,002	1,302
Total	5,727		1,302	800	9,143	1,302	729
Loans:
Ending balance: individually evaluated for impairment					14,298	13,612
Ending balance: collectively evaluated for impairment					1,651,593	1,496,237
Total loans and leases					1,665,891	1,509,849
Financing Receivable | Consumer credit products
Allowance for Credit Losses [Roll Forward]
Beginning balance	1,151		785
Provision (recovery) for loan losses	163		529
Charge offs	0		0
Recoveries	0		0
Ending balance	1,314		1,314
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					1,314	785
Total	1,151		785		1,314	785
Loans:
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					139,617	80,605
Total loans and leases					139,617	80,605
Financing Receivable | Other consumer finance
Allowance for Credit Losses [Roll Forward]
Beginning balance	4,222		2,820
Provision (recovery) for loan losses	3,336		6,359
Charge offs	(2,456)		(4,079)
Recoveries	28		30
Ending balance	5,130		5,130
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					5,130	2,820
Total	4,222		2,820		5,130	2,820
Loans:
Ending balance: individually evaluated for impairment					1,236	0
Ending balance: collectively evaluated for impairment					169,588	189,756
Total loans and leases					170,824	189,756
Financing Receivable | Consumer finance
Allowance for Credit Losses [Roll Forward]
Beginning balance	5,373		3,605
Provision (recovery) for loan losses	3,499		6,888
Charge offs	(2,456)		(4,079)
Recoveries	28		30
Ending balance	6,444		6,444
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					6,444	3,605
Total	5,373		3,605		6,444	3,605
Loans:
Ending balance: individually evaluated for impairment					1,236	0
Ending balance: collectively evaluated for impairment					309,205	270,361
Total loans and leases					310,441	270,361
Financing Receivable | Tax services
Allowance for Credit Losses [Roll Forward]
Beginning balance	1,546		0	5
Provision (recovery) for loan losses	22,473	18,129	23,969	19,146
Charge offs	(1)	0	(43)	0
Recoveries	84	9	176	422
Ending balance	24,102		24,102	19,573
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					24,102	0
Total	1,546		0	5	24,102	0	1,435
Loans:
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					84,824	1,073
Total loans and leases					84,824	1,073
Financing Receivable | Warehouse finance
Allowance for Credit Losses [Roll Forward]
Beginning balance	176		65
Provision (recovery) for loan losses	9		120
Charge offs	0		0
Recoveries	0		0
Ending balance	185		185
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					185	65
Total	176		65		185	65
Loans:
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					186,697	65,000
Total loans and leases					186,697	65,000
Financing Receivable | National Lending
Allowance for Credit Losses [Roll Forward]
Beginning balance	12,822		4,972	805
Provision (recovery) for loan losses	33,068	18,343	41,917	19,411
Charge offs	(6,503)	(339)	(9,306)	(468)
Recoveries	487	155	2,291	575
Ending balance	39,874		39,874	20,323
Ending balance: individually evaluated for impairment					141	0
Ending balance: collectively evaluated for impairment					39,733	4,972
Total	12,822		4,972	805	39,874	4,972	2,164
Loans:
Ending balance: individually evaluated for impairment					15,534	13,612
Ending balance: collectively evaluated for impairment					2,232,319	1,832,671
Total loans and leases					2,247,853	1,846,283
Loans Receivable
Allowance for Credit Losses [Roll Forward]
Beginning balance	8,468		8,068	6,729
Provision (recovery) for loan losses	250	0	500	0
Charge offs	(20)	0	(20)	(31)
Recoveries	100	57	250	57
Ending balance	8,798		8,798	6,755
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					8,798	8,068
Total	8,468		8,068	6,729	8,798	8,068	6,698
Loans:
Ending balance: individually evaluated for impairment					1,354	1,999
Ending balance: collectively evaluated for impairment					1,185,809	1,096,707
Total loans and leases					1,187,163	1,098,706
Loans Receivable | Unallocated
Allowance for Credit Losses [Roll Forward]
Beginning balance				526
Provision (recovery) for loan losses		89		463
Charge offs		0		0
Recoveries		0		0
Ending balance				989
Total				526			900
Loans Receivable | Commercial real estate and operating
Allowance for Credit Losses [Roll Forward]
Beginning balance	6,570		6,220	2,820
Provision (recovery) for loan losses	103	951	453	1,280
Charge offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	6,673		6,673	4,100
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					6,673	6,220
Total	6,570		6,220	2,820	6,673	6,220	3,149
Loans:
Ending balance: individually evaluated for impairment					0	451
Ending balance: collectively evaluated for impairment					869,917	790,439
Total loans and leases					869,917	790,890
Loans Receivable | 1-4 Family Real Estate
Allowance for Credit Losses [Roll Forward]
Beginning balance	719		632	809
Provision (recovery) for loan losses	259	233	346	120
Charge offs	(20)	0	(20)	(31)
Recoveries	0	3	0	3
Ending balance	958		958	901
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					958	632
Total	719		632	809	958	632	665
Loans:
Ending balance: individually evaluated for impairment					134	94
Ending balance: collectively evaluated for impairment					256,945	247,224
Total loans and leases					257,079	247,318
Loans Receivable | Agricultural real estate and operating
Allowance for Credit Losses [Roll Forward]
Beginning balance	1,179		1,216	2,574
Provision (recovery) for loan losses	(112)	(1,273)	(299)	(1,863)
Charge offs	0	0	0	0
Recoveries	100	$ 54	250	54
Ending balance	1,167		1,167	765
Ending balance: individually evaluated for impairment					0	0
Ending balance: collectively evaluated for impairment					1,167	1,216
Total	$ 1,179		$ 1,216	$ 2,574	1,167	1,216	$ 1,984
Loans:
Ending balance: individually evaluated for impairment					1,220	1,454
Ending balance: collectively evaluated for impairment					58,947	59,044
Total loans and leases					$ 60,167	$ 60,498