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LOANS - Summary of Sector Attributes of Commercial Real Estate Investments (Details) - Commercial Mortgage - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
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SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Loans | $ 1,384,122 | $ 1,372,430 | $ 1,618,794
Percentage of Loan Portfolio | 100.00% | 100.00% |
Office |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Loans | $ 577,893 | $ 650,034 |
Percentage of Loan Portfolio | 41.80% | 47.40% |
Retail |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Loans | $ 249,917 | $ 256,493 |
Percentage of Loan Portfolio | 18.10% | 18.70% |
Multifamily |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Loans | $ 217,131 | $ 250,095 |
Percentage of Loan Portfolio | 15.70% | 18.20% |
Hotel |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Loans | $ 130,578 | $ 115,536 |
Percentage of Loan Portfolio | 9.40% | 8.40% |
Industrial |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Loans | $ 114,152 | $ 60,097 |
Percentage of Loan Portfolio | 8.20% | 4.40% |
Other |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Loans | $ 75,306 | $ 20,302 |
Percentage of Loan Portfolio | 5.40% | 1.50% |
Healthcare |  |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |  |
Loans | $ 19,145 | $ 19,873 |
Percentage of Loan Portfolio | 1.40% | 1.40% |

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- Definition Percent of net assets at close of period. For schedules of investments that are categorized, each category has a percent of net assets for the aggregated value of the Investments in the category. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-12B(Column D)) -URI http://asc.fasb.org/extlink&oid=120401592&loc=d3e611197-123010 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 210 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841 + Details
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- Definition Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 310 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-29(Column G)) -URI http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014 + Details
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