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Summary of Significant Accounting Policies (Income Tax) (Details) - USD ($) | 3 Months Ended
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Mar. 31, 2021 | Mar. 31, 2020
Accounting Policies [Abstract] |  |
Percentage of annual REIT taxable income distributed to stockholders | 100.00% |
REIT income tax expense | $ 0 |
Deferred income tax expense (benefit) | 0 | $ 0
Valuation allowance decrease | $ 74,400,000 |

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