| **INVESTMENT SECURITIES (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Thousands** | Sep. 30, 2015 | Dec. 31, 2014 |
|--------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | $ 2,726,258   | $ 2,622,575   |
| 12 months or longer                                                                                                                  | 3,507,119     | 4,934,027     |
| Total                                                                                                                                | 6,233,377     | 7,556,602     |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (16,480)      | (12,187)      |
| 12 months or longer                                                                                                                  | (106,765)     | (173,192)     |
| Total                                                                                                                                | (123,245)     | (185,379)     |
| US Treasury securities                                                                                                               |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  |          | 298,914       |
| 12 months or longer                                                                                                                  |          | 0             |
| Total                                                                                                                                |          | 298,914       |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  |          | (56)          |
| 12 months or longer                                                                                                                  |          | 0             |
| Total                                                                                                                                | 0             | (56)          |
| Corporate debt securities                                                                                                            |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 500,998       | 538,108       |
| 12 months or longer                                                                                                                  | 136,932       | 214,852       |
| Total                                                                                                                                | 637,930       | 752,960       |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (6,427)       | (3,262)       |
| 12 months or longer                                                                                                                  | (1,914)       | (3,648)       |
| Total                                                                                                                                | (8,341)       | (6,910)       |
| Asset-backed securities                                                                                                              |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 143,150       | 632,936       |
| 12 months or longer                                                                                                                  | 0             | 424,333       |
| Total                                                                                                                                | 143,150       | 1,057,269     |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (1,041)       | (1,437)       |
| 12 months or longer                                                                                                                  | 0             | (3,154)       |
| Total                                                                                                                                | (1,041)       | (4,591)       |
| Equity securities                                                                                                                    |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 376           | 55            |
| 12 months or longer                                                                                                                  | 9,850         | 9,879         |
| Total                                                                                                                                | 10,226        | 9,934         |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (2)           | 0             |
| 12 months or longer                                                                                                                  | (299)         | (279)         |
| Total                                                                                                                                | (301)         | (279)         |
| State and municipal securities                                                                                                       |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 203,170       | 45,128        |
| 12 months or longer                                                                                                                  | 25,430        | 192,091       |
| Total                                                                                                                                | 228,600       | 237,219       |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (1,217)       | (90)          |
| 12 months or longer                                                                                                                  | (931)         | (2,295)       |
| Total                                                                                                                                | (2,148)       | (2,385)       |
| U.S. government agencies - Residential                                                                                               |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 400,513       | 415,731       |
| 12 months or longer                                                                                                                  | 972,042       | 1,348,908     |
| Total                                                                                                                                | 1,372,555     | 1,764,639     |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (735)         | (2,693)       |
| 12 months or longer                                                                                                                  | (15,989)      | (31,118)      |
| Total                                                                                                                                | (16,724)      | (33,811)      |
| U.S. government agencies - Commercial                                                                                                |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 216,806       | 281,258       |
| 12 months or longer                                                                                                                  | 116,893       | 136,269       |
| Total                                                                                                                                | 333,699       | 417,527       |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (2,551)       | (2,459)       |
| 12 months or longer                                                                                                                  | (2,558)       | (4,727)       |
| Total                                                                                                                                | (5,109)       | (7,186)       |
| FHLMC and FNMA - Residential                                                                                                         |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 1,219,050     | 399,176       |
| 12 months or longer                                                                                                                  | 2,245,972     | 2,607,695     |
| Total                                                                                                                                | 3,465,022     | 3,006,871     |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (4,080)       | (2,019)       |
| 12 months or longer                                                                                                                  | (85,074)      | (127,971)     |
| Total                                                                                                                                | (89,154)      | (129,990)     |
| FHLMC and FNMA - Commercial                                                                                                          |          |          |
| **Fair Value**                                                                                                                       |          |          |
| Less than 12 months                                                                                                                  | 42,195        | 11,269        |
| 12 months or longer                                                                                                                  | 0             | 0             |
| Total                                                                                                                                | 42,195        | 11,269        |
| **Unrealized Losses**                                                                                                                |          |          |
| Less than 12 months                                                                                                                  | (427)         | (171)         |
| 12 months or longer                                                                                                                  | 0             | 0             |
| Total                                                                                                                                | $ (427)       | $ (171)       |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.
+ References
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| - Definition
This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.
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| - Definition
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