FAIR VALUE MEASUREMENTS - Assets Measured at Fair Value on Recurring and Non-recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Sep. 30, 2018
Available-for-sale debt securities [Abstract]
Mortgage-backed securities available for sale, at fair value	$ 413,493	$ 364,065
Total available for sale securities	1,495,156	1,852,025
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Total held to maturity securities	149,164	160,563
Level 1
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Available-for-sale debt securities [Abstract]
Total available for sale securities	0	3,800
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Total held to maturity securities	0	0
Level 2
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Available-for-sale debt securities [Abstract]
Total available for sale securities	1,495,156	1,848,225
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Total held to maturity securities	149,164	160,974
Level 3
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3,365,283	2,927,755
Available-for-sale debt securities [Abstract]
Total available for sale securities	0	0
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Total held to maturity securities	0	0
Nonrecurring
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	30,802	36,463
Nonrecurring \| Level 1
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Nonrecurring \| Level 2
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Nonrecurring \| Level 3
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	30,802	36,463
Recurring
Available-for-sale debt securities [Abstract]
Small business administration securities	164,103	44,337
Obligations of states and political subdivisions	11,529	16,910
Non-bank qualified obligations of states and political subdivisions	621,642	1,109,885
Asset-baked securities	284,389	313,028
Mortgage-backed securities	413,493	364,065
Mortgage-backed securities available for sale, at fair value	1,495,156	1,848,225
Common equities and mutual funds	4,211	3,800
Total available for sale securities		1,852,025
Recurring \| Level 1
Available-for-sale debt securities [Abstract]
Small business administration securities	0	0
Obligations of states and political subdivisions	0	0
Non-bank qualified obligations of states and political subdivisions	0	0
Asset-baked securities	0	0
Mortgage-backed securities	0	0
Mortgage-backed securities available for sale, at fair value	0	0
Common equities and mutual funds	4,211	3,800
Total available for sale securities		3,800
Recurring \| Level 2
Available-for-sale debt securities [Abstract]
Small business administration securities	164,103	44,337
Obligations of states and political subdivisions	11,529	16,910
Non-bank qualified obligations of states and political subdivisions	621,642	1,109,885
Asset-baked securities	284,389	313,028
Mortgage-backed securities	413,493	364,065
Mortgage-backed securities available for sale, at fair value	1,495,156	1,848,225
Common equities and mutual funds	0	0
Total available for sale securities		1,848,225
Recurring \| Level 3
Available-for-sale debt securities [Abstract]
Small business administration securities	0	0
Obligations of states and political subdivisions	0	0
Non-bank qualified obligations of states and political subdivisions	0	0
Asset-baked securities	0	0
Mortgage-backed securities	0	0
Mortgage-backed securities available for sale, at fair value	0	0
Common equities and mutual funds	0	0
Total available for sale securities		0
Asset based lending \| Nonrecurring
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,218	57
Asset based lending \| Nonrecurring \| Level 1
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Asset based lending \| Nonrecurring \| Level 2
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Asset based lending \| Nonrecurring \| Level 3
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,218	57
Factoring \| Nonrecurring
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	13	1,899
Factoring \| Nonrecurring \| Level 1
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Factoring \| Nonrecurring \| Level 2
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Factoring \| Nonrecurring \| Level 3
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	13	1,899
Lease financing \| Nonrecurring
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	23	2,869
Lease financing \| Nonrecurring \| Level 1
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Lease financing \| Nonrecurring \| Level 2
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Lease financing \| Nonrecurring \| Level 3
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	23	2,869
Commercial Portfolio Segment \| Nonrecurring
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,254	4,825
Commercial Portfolio Segment \| Nonrecurring \| Level 1
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Commercial Portfolio Segment \| Nonrecurring \| Level 2
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0	0
Commercial Portfolio Segment \| Nonrecurring \| Level 3
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 1,254	$ 4,825

Fair value of asset backed securities investments classified as available for sale.

No definition available.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents common equities and mutual funds as of the balance sheet date which have been categorized as available-for-sale.

+ References

No definition available.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents non-bank qualified obligations of states and political subdivision as of the balance sheet date which have been categorized as available-for-sale.

+ References

No definition available.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents obligations of states and political subdivision as of the balance sheet date which have been categorized as available-for-sale.

+ References

No definition available.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents debt securities issued by the Small Business Administration (SBA) as of the balance sheet date which have been categorized as available-for-sale.

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No definition available.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

No definition available.

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- References

No definition available.

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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- Definition

Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as available-for-sale.

+ References

No definition available.

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