| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (Narrative) (Details) $ in Thousands**                                                                                                                                                                                                                                                                                                                              | 3 Months Ended | 9 Months Ended | 12 Months Ended |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|-----------------|
||
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                           |                |           |            |   |
| Loans pledged as collateral                                                                                                                                                                                                                                                                                                                                                                                 |                | $ 59,100,000   | $ 59,100,000    | $ 52,500,000 |
| Loans held-for-sale                                                                                                                                                                                                                                                                                                                                                                                         | [1]            | 2,990,708      | 2,990,708       | 260,252 |
| Accrued interest receivable                                                                                                                                                                                                                                                                                                                                                                                 | [2]            | 586,350        | 586,350         | 559,962 |
| Troubled debt restructurings                                                                                                                                                                                                                                                                                                                                                                                |                | 3,957,659      | $ 3,957,659     | 2,495,028 |
| TDRs, number of days past due after modification considered to have subsequently defaulted                                                                                                                                                                                                                                                                                                                  |                |           | 90 days         |   |
| Performing                                                                                                                                                                                                                                                                                                                                                                                                  |                |           |            |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                           |                |           |            |   |
| Interest income                                                                                                                                                                                                                                                                                                                                                                                             |                |           | $ 187,900       | 86,100 |
| Troubled debt restructurings                                                                                                                                                                                                                                                                                                                                                                                |                | 3,434,409      | 3,434,409       | 2,117,789 |
| Loans receivable                                                                                                                                                                                                                                                                                                                                                                                            |                |           |            |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                           |                |           |            |   |
| Accrued interest receivable                                                                                                                                                                                                                                                                                                                                                                                 |                | 521,900        | 521,900         | $ 492,700 |
| Multi-family loans | FNMA                                                                                                                                                                                                                                                                                                                                                                                   |                |           |            |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                           |                |           |            |   |
| Performing multi-family loans purchased from FNMA                                                                                                                                                                                                                                                                                                                                                           |                | 1,400,000      | $ 1,400,000     |   |
| Commercial real estate loans | Commercial                                                                                                                                                                                                                                                                                                                                                                   |                |           |            |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                           |                |           |            |   |
| Number of business lines | business_line                                                                                                                                                                                                                                                                                                                                                                    |                |           | 3               |   |
| Personal unsecured loans                                                                                                                                                                                                                                                                                                                                                                                    |                |           |            |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                           |                |           |            |   |
| Transfer of loans to held-for-sale                                                                                                                                                                                                                                                                                                                                                                          |                | $ 1,900,000    |            |   |
| Retail installment contracts                                                                                                                                                                                                                                                                                                                                                                                |                |           |            |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                           |                |           |            |   |
| TDRs, number of days past due after modification considered to have subsequently defaulted                                                                                                                                                                                                                                                                                                                  |                |           | 120 days        |   |
|                                                                                                                                                                                                                                                                                                                                                                                                             |
| [1]Recorded at the fair value option ("FVO") or lower of cost or fair value.[2]The Company has interests in certain securitization trusts ("Trusts") that are considered variable interest entities ("VIEs") for accounting purposes. The Company consolidates VIEs where it is deemed the primary beneficiary. See Note 7 to these Condensed Consolidated Financial Statements for additional information. |

| X                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans Sold with Recourse, Repurchase Amount
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| X                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of Business Lines
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| X                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Transfer of Loans to Held-for-sale
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No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Troubled Debt Restructuring, Number of Days Past Due After Modification Considered Subsequently Defaulted
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| - Definition
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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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The gross interest income that would have been recorded in the period on troubled debt restructurings, if the loans had been current in accordance with their original terms and had been outstanding throughout the period or since origination, if held for part of the period.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.
+ References
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