| **INVESTMENT SECURITIES (Gains (Losses) and Proceeds on Sale of Securities) (Details) - USD ($)** | 3 Months Ended | 6 Months Ended | 9 Months Ended |
|---------------------------------------------------------------------------------------------------|----------------|----------------|----------------|
||
| **Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract]**             |           |           |           |   |   |   |
| Proceeds from the sales of available-for-sale securities                                          | $ 497,182,000  |           | $ 21,138,000   |   | $ 2,751,790,000 | $ 311,019,000 |
| Gross realized gains                                                                              | 533,000        |           | 131,000        |   | 23,592,000 | 11,547,000 |
| Gross realized losses                                                                             | (2,526,000)    |           | 0              |   | (5,229,000) | (67,000) |
| OTTI                                                                                              | 0              | $ 0            | 0              | $ (1,100,000) | (1,092,000) | 0 |
| Net realized (losses)/gains                                                                       | (1,993,000)    |           | 131,000        |   | 17,271,000 | 11,480,000 |
| Corporate debt securities                                                                         |           |           |           |   |   |   |
| **Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract]**             |           |           |           |   |   |   |
| Investment securities sold during the period                                                      | 63,700,000     |           | 88,400,000     |   | 517,600,000 | 434,800,000 |
| Realized investment gain (loss)                                                                   | 400,000        |           | $ 100,000      |   | 7,000,000 | 4,700,000 |
| Asset-backed securities                                                                           |           |           |           |   |   |   |
| **Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract]**             |           |           |           |   |   |   |
| Investment securities sold during the period                                                      | 419,600,000    |           |           |   | 683,900,000 |   |
| Realized investment gain (loss)                                                                   | $ (1,400,000)  |           |           |   | (200,000) |   |
| State and municipal securities                                                                    |           |           |           |   |   |   |
| **Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract]**             |           |           |           |   |   |   |
| Investment securities sold during the period                                                      |           |           |           |   | 421,500,000 | 89,000,000 |
| Realized investment gain (loss)                                                                   |           |           |           |   | $ 12,100,000 | 5,200,000 |
| Mortgage backed securities                                                                        |           |           |           |   |   |   |
| **Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract]**             |           |           |           |   |   |   |
| Investment securities sold during the period                                                      |           |           |           |   |   | 21,600,000 |
| Realized investment gain (loss)                                                                   |           |           |           |   |   | $ 1,300,000 |

| X                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Book value of securities designated for sale and sold.
+ References
No definition available.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.
+ References
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