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LOANS - Additional Information (Details) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 USD ($) loan | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Jan. 01, 2020 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Assets | $ 88,455,103,000 | $ 130,295,081,000 |  |
Loan loss provision | 147,581,000 | 16,569,000 | $ 3,496,000 |
Allowance for loan loss | 169,500,000 | $ 20,100,000 |  |
Loans | $ 498,081,000 |  |  |
Loans receivable with variable rates of interest | 94.00% | 92.00% |  |
Cumulative Effect, Period of Adoption, Adjustment |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Allowance for loan loss |  | $ 37,400,000 |  |
Residential Mortgage Loans |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Assets | $ 300,000,000 | 1,600,000,000 |  |
Loans | $ 47,000,000.0 | $ 66,700,000 |  |
Percent of adjustable-rate loans | 37.00% | 36.00% |  |
Commercial Mortgage Loans |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Loan loss provision | $ 78,400,000 | $ 9,200,000 |  |
Aggregate principal balance | 181,200,000 | 43,600,000 |  |
Carrying value | $ 113,600,000 | 30,900,000 |  |
Number of contracts modified | loan | 5 |  |  |
Number of contracts modified, partial paydowns | loan | 2 |  |  |
Restructuring, partial paydowns | $ 4,500,000 |  |  |
Future funding commitments | 4,100,000 |  |  |
Amortized cost basis, nonaccrual | 46,800,000 | 175,200,000 |  |
Interest income, nonaccrual | 2,100,000 | (100,000) |  |
Unfunded corporate loan commitments | 99,300,000 | 181,400,000 |  |
Expected gain (loss) on unfunded commitments | 5,100,000 |  |  |
Restructuring, carrying value | 243,800,000 |  |  |
Commercial Mortgage Loans | Extended Maturity |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Allowance for loan loss | $ 23,600,000 |  |  |
Number of contracts modified | loan | 4 |  |  |
Commercial Mortgage Loans | Payment Deferral |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Number of contracts modified | loan | 1 |  |  |
Forbearance term | 120 days |  |  |
Commercial Mortgage Loans | Cumulative Effect, Period of Adoption, Adjustment |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Allowance for loan loss |  |  |  | $ 7,800,000
Commercial Mortgage Loans | Cumulative Effect, Period of Adoption, Adjusted Balance |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Loan loss provision | $ 54,800,000 |  |  |
Corporate Loans |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Loan loss provision | 4,500,000 | 7,400,000 | $ 0 |
Aggregate principal balance |  | 19,600,000 |  |
Carrying value |  | 12,200,000 |  |
Loans | 2,239,930,000 | 2,144,850,000 |  |
Amortized cost basis, nonaccrual | 0.0 | 12,200,000 |  |
Interest income, nonaccrual | 0.0 | 1,500,000 |  |
Unfunded corporate loan commitments | 87,300,000 | 81,200,000 |  |
Debt instrument face amount | 4,800,000 |  |  |
Write offs | 11,900,000 |  |  |
Expected gain (loss) on unfunded commitments | 700,000 |  |  |
Corporate Loans | Second lien loans |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Loans | 750,805,000 | 748,710,000 |  |
Debt instrument face amount | 2,800,000 |  |  |
Corporate Loans | First lien loans |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Loans | 1,489,125,000 | $ 1,396,140,000 |  |
Write offs | 19,600,000 |  |  |
Corporate Loans | Cumulative Effect, Period of Adoption, Adjustment |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Allowance for loan loss |  |  |  | $ 29,700,000
Corporate Loans | Cumulative Effect, Period of Adoption, Adjusted Balance |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Loan loss provision | $ 9,900,000 |  |  |
Minimum | Corporate Loans |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Senior secured loans, stated maturity | 5 years |  |  |
Maximum | Corporate Loans |  |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |  |
Senior secured loans, stated maturity | 7 years |  |  |

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