SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Concentration of Risk (Details) - property
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9 Months Ended |
12 Months Ended |
Sep. 30, 2021 |
Sep. 30, 2020 |
Dec. 31, 2020 |
| Product Information [Line Items] |
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| Number of real estate properties |
89
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89
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| Real estate property at Florida |
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| Product Information [Line Items] |
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| Real estate portfolio (as a percent) |
11.00%
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17.00%
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| Real estate property at North Carolina |
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| Product Information [Line Items] |
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| Real estate portfolio (as a percent) |
11.00%
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|
15.00%
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| Minimum | Real estate property at Texas |
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| Product Information [Line Items] |
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| Real estate portfolio (as a percent) |
10.00%
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| Minimum | Real Estate property at Oregon and Michigan |
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| Product Information [Line Items] |
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| Real estate portfolio (as a percent) |
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10.00%
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| Customer Concentration Risk | Hilton Grand Vacations | Consolidated revenues |
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| Product Information [Line Items] |
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| Concentration risk (as a percent) |
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13.00%
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| Customer Concentration Risk | Wells Fargo Bank, NA | Consolidated revenues |
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| Product Information [Line Items] |
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| Concentration risk (as a percent) |
13.00%
|
20.00%
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