FAIR VALUE MEASUREMENTS - Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Sep. 30, 2018
Financial assets [Abstract]
Securities available for sale	$ 1,495,156	$ 1,852,025
Securities held to maturity	149,164	160,563
Equity Securities, FV-NI	1,900
Financial liabilities [Abstract]
Long-term debt	99,800	88,963
Subordinated debentures	11,583	425,759
Level 1
Financial assets [Abstract]
Cash and cash equivalents	156,461	99,977
Securities available for sale	0	3,800
Securities held to maturity	0	0
Equity Securities, FV-NI	4,211
Total securities	4,211	3,800
Trade and Loans Receivables Held-for-sale, Net, Not Part of Disposal Group	0	0
Loans receivable [Abstract]
Total loans receivable	0	0
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	0	0
Accrued interest receivable, fair value disclosure	20,281	22,016
Financial liabilities [Abstract]
Noninterest bearing demand deposits	3,034,428	2,405,274
Interest bearing demand deposits, savings, and money markets	300,033	218,347
Certificates of deposit	0	0
Deposits, Wholesale, Non-Maturing	207,795	94,384
Deposits, Wholesale, Certificates of Deposit	0	0
Total deposits	3,542,256	2,718,005
Federal fund purchased		422,000
Securities sold under agreements to repurchase	0	0
Long-term debt	0	0
Trust Preferred Securities	0	0
Subordinated debentures	0	0
Other borrowings	0
Accrued interest payable	9,239	7,794
Level 2
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	1,495,156	1,848,225
Securities held to maturity	149,164	160,974
Equity Securities, FV-NI	0
Total securities	1,644,320	2,009,199
Trade and Loans Receivables Held-for-sale, Net, Not Part of Disposal Group	59,745	15,606
Loans receivable [Abstract]
Total loans receivable	0	0
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	7,436	23,400
Accrued interest receivable, fair value disclosure	0	0
Financial liabilities [Abstract]
Noninterest bearing demand deposits	0	0
Interest bearing demand deposits, savings, and money markets	0	0
Certificates of deposit	153,951	273,800
Deposits, Wholesale, Non-Maturing	0	0
Deposits, Wholesale, Certificates of Deposit	1,272,291	1,432,146
Total deposits	1,426,242	1,705,946
Federal fund purchased		0
Securities sold under agreements to repurchase	2,804	3,694
Long-term debt	1,996	1,876
Trust Preferred Securities	13,878	13,866
Subordinated debentures	75,188	75,563
Other borrowings	19,162
Accrued interest payable	0	0
Level 3
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	0	0
Securities held to maturity	0	0
Equity Securities, FV-NI	0
Total securities	0	0
Trade and Loans Receivables Held-for-sale, Net, Not Part of Disposal Group	0	0
Loans receivable [Abstract]
Total loans receivable	3,365,283	2,927,755
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	0	0
Accrued interest receivable, fair value disclosure	0	0
Financial liabilities [Abstract]
Noninterest bearing demand deposits	0	0
Interest bearing demand deposits, savings, and money markets	0	0
Certificates of deposit	0	0
Deposits, Wholesale, Non-Maturing	0	0
Deposits, Wholesale, Certificates of Deposit	0	0
Total deposits	0	0
Federal fund purchased		0
Securities sold under agreements to repurchase	0	0
Long-term debt	0	0
Trust Preferred Securities	0	0
Subordinated debentures	0	0
Other borrowings	0
Accrued interest payable	0	0
Carrying Amount
Financial assets [Abstract]
Cash and cash equivalents	156,461	99,977
Securities available for sale	1,495,156	1,852,025
Securities held to maturity	154,598	172,154
Equity Securities, FV-NI	4,211
Total securities	1,653,965	2,024,179
Trade and Loans Receivables Held-for-sale, Net, Not Part of Disposal Group	59,745	15,606
Loans receivable [Abstract]
Total loans receivable	3,435,016	2,944,989
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	7,436	23,400
Accrued interest receivable, fair value disclosure	20,281	22,016
Financial liabilities [Abstract]
Noninterest bearing demand deposits	3,034,428	2,405,274
Interest bearing demand deposits, savings, and money markets	300,033	218,347
Certificates of deposit	154,401	276,180
Deposits, Wholesale, Non-Maturing	207,795	94,384
Deposits, Wholesale, Certificates of Deposit	1,273,650	1,436,802
Total deposits	4,970,307	4,430,987
Federal fund purchased		422,000
Securities sold under agreements to repurchase	2,804	3,694
Long-term debt	1,996	1,876
Trust Preferred Securities	13,661	13,661
Subordinated debentures	73,566	73,491
Other borrowings	19,357
Accrued interest payable	9,239	7,794
Estimated Fair Value
Financial assets [Abstract]
Cash and cash equivalents	156,461	99,977
Securities available for sale	1,495,156	1,852,025
Securities held to maturity	149,164	160,974
Equity Securities, FV-NI	4,211
Total securities	1,648,531	2,012,999
Trade and Loans Receivables Held-for-sale, Net, Not Part of Disposal Group	59,745	15,606
Loans receivable [Abstract]
Total loans receivable	3,365,283	2,927,755
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure	7,436	23,400
Accrued interest receivable, fair value disclosure	20,281	22,016
Financial liabilities [Abstract]
Noninterest bearing demand deposits	3,034,428	2,405,274
Interest bearing demand deposits, savings, and money markets	300,033	218,347
Certificates of deposit	153,951	273,800
Deposits, Wholesale, Non-Maturing	207,795	94,384
Deposits, Wholesale, Certificates of Deposit	1,272,291	1,432,146
Total deposits	4,968,498	4,423,951
Federal fund purchased		422,000
Securities sold under agreements to repurchase	2,804	3,694
Long-term debt	1,996	1,876
Trust Preferred Securities	13,878	13,866
Subordinated debentures	75,188	75,563
Other borrowings	19,162
Accrued interest payable	9,239	7,794
Loans Receivable | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Level 3
Loans receivable [Abstract]
Total loans receivable	1,174,620	1,076,782
Loans Receivable | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	1,187,163	1,098,706
Loans Receivable | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	1,174,620	1,076,782
Loans Receivable | SBA/USDA | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | SBA/USDA | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | SBA/USDA | Level 3
Loans receivable [Abstract]
Total loans receivable	74,407	61,072
Loans Receivable | SBA/USDA | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	77,481	59,374
Loans Receivable | SBA/USDA | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	74,407	61,072
Loans Receivable | Other commercial finance | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Other commercial finance | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Other commercial finance | Level 3
Loans receivable [Abstract]
Total loans receivable	100,038	83,111
Loans Receivable | Other commercial finance | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	98,956	85,145
Loans Receivable | Other commercial finance | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	100,038	83,111
Loans Receivable | Commercial finance | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Commercial finance | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Commercial finance | Level 3
Loans receivable [Abstract]
Total loans receivable	1,637,504	1,506,969
Loans Receivable | Commercial finance | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	1,665,891	1,509,849
Loans Receivable | Commercial finance | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	1,637,504	1,506,969
Loans Receivable | Consumer credit products | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Consumer credit products | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Consumer credit products | Level 3
Loans receivable [Abstract]
Total loans receivable	138,748	80,633
Loans Receivable | Consumer credit products | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	139,617	80,605
Loans Receivable | Consumer credit products | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	138,748	80,633
Loans Receivable | Other consumer finance | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Other consumer finance | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Other consumer finance | Level 3
Loans receivable [Abstract]
Total loans receivable	166,925	197,320
Loans Receivable | Other consumer finance | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	170,824	189,756
Loans Receivable | Other consumer finance | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	166,925	197,320
Loans Receivable | Consumer finance | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Consumer finance | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Consumer finance | Level 3
Loans receivable [Abstract]
Total loans receivable	305,673	277,953
Loans Receivable | Consumer finance | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	310,441	270,361
Loans Receivable | Consumer finance | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	305,673	277,953
Loans Receivable | Tax services | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Tax services | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Tax services | Level 3
Loans receivable [Abstract]
Total loans receivable	60,722	1,073
Loans Receivable | Tax services | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	84,824	1,073
Loans Receivable | Tax services | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	60,722	1,073
Loans Receivable | Warehouse finance | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Warehouse finance | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Warehouse finance | Level 3
Loans receivable [Abstract]
Total loans receivable	186,764	64,978
Loans Receivable | Warehouse finance | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	186,697	65,000
Loans Receivable | Warehouse finance | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	186,764	64,978
Loans Receivable | National Lending | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | National Lending | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | National Lending | Level 3
Loans receivable [Abstract]
Total loans receivable	2,190,663	1,850,973
Loans Receivable | National Lending | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	2,247,853	1,846,283
Loans Receivable | National Lending | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	2,190,663	1,850,973
Loans Receivable | Commercial Real Estate and Operating [Member] | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Commercial Real Estate and Operating [Member] | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Commercial Real Estate and Operating [Member] | Level 3
Loans receivable [Abstract]
Total loans receivable	861,524	773,203
Loans Receivable | Commercial Real Estate and Operating [Member] | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	869,917	790,890
Loans Receivable | Commercial Real Estate and Operating [Member] | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	861,524	773,203
Loans Receivable | 1-4 Family Real Estate | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | 1-4 Family Real Estate | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | 1-4 Family Real Estate | Level 3
Loans receivable [Abstract]
Total loans receivable	254,642	244,730
Loans Receivable | 1-4 Family Real Estate | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	257,079	247,318
Loans Receivable | 1-4 Family Real Estate | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	254,642	244,730
Loans Receivable | Agricultural Real Estate | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Agricultural Real Estate | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Loans Receivable | Agricultural Real Estate | Level 3
Loans receivable [Abstract]
Total loans receivable	58,454	58,849
Loans Receivable | Agricultural Real Estate | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	60,167	60,498
Loans Receivable | Agricultural Real Estate | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	58,454	58,849
Financing Receivable | Asset based lending | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Financing Receivable | Asset based lending | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Financing Receivable | Asset based lending | Level 3
Loans receivable [Abstract]
Total loans receivable	551,579	477,471
Financing Receivable | Asset based lending | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	572,210	477,917
Financing Receivable | Asset based lending | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	551,579	477,471
Financing Receivable | Factoring | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Financing Receivable | Factoring | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Financing Receivable | Factoring | Level 3
Loans receivable [Abstract]
Total loans receivable	283,337	283,424
Financing Receivable | Factoring | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	287,955	284,221
Financing Receivable | Factoring | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	283,337	283,424
Financing Receivable | Lease financing | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Financing Receivable | Lease financing | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Financing Receivable | Lease financing | Level 3
Loans receivable [Abstract]
Total loans receivable	320,411	264,679
Financing Receivable | Lease financing | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	321,414	265,315
Financing Receivable | Lease financing | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	320,411	264,679
Financing Receivable | Insurance premium finance | Level 1
Loans receivable [Abstract]
Total loans receivable	0	0
Financing Receivable | Insurance premium finance | Level 2
Loans receivable [Abstract]
Total loans receivable	0	0
Financing Receivable | Insurance premium finance | Level 3
Loans receivable [Abstract]
Total loans receivable	307,732	337,212
Financing Receivable | Insurance premium finance | Carrying Amount
Loans receivable [Abstract]
Total loans receivable	307,875	337,877
Financing Receivable | Insurance premium finance | Estimated Fair Value
Loans receivable [Abstract]
Total loans receivable	$ 307,732	$ 337,212