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Summary of Significant Accounting Policies (Income Taxes) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Tax Treatment Of Dividend |  |  |
Internal taxable income distribution policy (in percentage) | 100.00% |  |
Differences between book and tax basis | $ 139,364 |  |
Reconciliation of Net Income to Estimated Taxable Income |  |  |
Net income | 41,939 | $ 60,075 | $ 32,844
Straight-line rent adjustments | 21,048 | 2,359 | 5,870
Depreciation and amortization | 2,112 | 2,751 | (6,586)
Change in fair value of marketable securities | 8,599 | 8,757 | 11,990
Loss from discontinued operations (see Note 6) | 0 | 0 | 23,797
Other | 7,677 | 137 | 440
Estimated taxable income | $ 81,375 | $ 74,079 | $ 68,355
Minimum |  |  |
Tax Treatment Of Dividend |  |  |
Real estate investment trust distributable income policy (in percentage) | 90.00% |  |
Ordinary Income |  |  |
Tax Treatment Of Dividend |  |  |
Payments of dividends net percent | 100.00% | 99.60% | 100.00%
Long Term Capital Gain |  |  |
Tax Treatment Of Dividend |  |  |
Payments of dividends net percent |  | 0.40% |

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