| **INVESTMENT SECURITIES (Gross Unrealized Loss and Fair Value of AFS Debt Securities) (Details) - USD ($) $ in Thousands** | Mar. 31, 2020 | Dec. 31, 2019 |
|----------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value**                                                                                                             |          |          |
| Less than 12 months                                                                                                        | $ 273,933     | $ 3,269,692   |
| 12 months or longer                                                                                                        | 123,750       | 2,903,310     |
| **Unrealized Losses**                                                                                                      |          |          |
| Less than 12 months                                                                                                        | (2,284)       | (12,994)      |
| 12 months or longer                                                                                                        | (2,371)       | (36,974)      |
| U.S. Treasury securities                                                                                                   |          |          |
| **Fair Value**                                                                                                             |          |          |
| Less than 12 months                                                                                                        | 0             | 200,096       |
| 12 months or longer                                                                                                        | 0             | 499,883       |
| **Unrealized Losses**                                                                                                      |          |          |
| Less than 12 months                                                                                                        | 0             | (167)         |
| 12 months or longer                                                                                                        | 0             | (125)         |
| Corporate debt securities                                                                                                  |          |          |
| **Fair Value**                                                                                                             |          |          |
| Less than 12 months                                                                                                        | 89,642        | 110,802       |
| 12 months or longer                                                                                                        | 0             | 0             |
| **Unrealized Losses**                                                                                                      |          |          |
| Less than 12 months                                                                                                        | (62)          | (22)          |
| 12 months or longer                                                                                                        | 0             | 0             |
| ABS                                                                                                                        |          |          |
| **Fair Value**                                                                                                             |          |          |
| Less than 12 months                                                                                                        | 26,080        | 27,662        |
| 12 months or longer                                                                                                        | 41,631        | 47,616        |
| **Unrealized Losses**                                                                                                      |          |          |
| Less than 12 months                                                                                                        | (66)          | (44)          |
| 12 months or longer                                                                                                        | (1,283)       | (1,429)       |
| GNMA - Residential                                                                                                         |          |          |
| **Fair Value**                                                                                                             |          |          |
| Less than 12 months                                                                                                        | 83,016        | 2,053,763     |
| 12 months or longer                                                                                                        | 32,753        | 997,024       |
| **Unrealized Losses**                                                                                                      |          |          |
| Less than 12 months                                                                                                        | (1,185)       | (6,895)       |
| 12 months or longer                                                                                                        | (295)         | (9,171)       |
| GNMA - Commercial                                                                                                          |          |          |
| **Fair Value**                                                                                                             |          |          |
| Less than 12 months                                                                                                        | 4,069         | 217,291       |
| 12 months or longer                                                                                                        | 2,458         | 14,300        |
| **Unrealized Losses**                                                                                                      |          |          |
| Less than 12 months                                                                                                        | (7)           | (1,756)       |
| 12 months or longer                                                                                                        | (5)           | (29)          |
| FHLMC and FNMA - Residential                                                                                               |          |          |
| **Fair Value**                                                                                                             |          |          |
| Less than 12 months                                                                                                        | 71,126        | 660,078       |
| 12 months or longer                                                                                                        | 46,481        | 1,344,057     |
| **Unrealized Losses**                                                                                                      |          |          |
| Less than 12 months                                                                                                        | (964)         | (4,110)       |
| 12 months or longer                                                                                                        | (784)         | (26,215)      |
| FHLMC and FNMA - Commercial                                                                                                |          |          |
| **Fair Value**                                                                                                             |          |          |
| Less than 12 months                                                                                                        | 0             | 0             |
| 12 months or longer                                                                                                        | 427           | 430           |
| **Unrealized Losses**                                                                                                      |          |          |
| Less than 12 months                                                                                                        | 0             | 0             |
| 12 months or longer                                                                                                        | $ (4)         | $ (5)         |

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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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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), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
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| - Definition
Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
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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), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
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