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Marketable Securities (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Marketable Securities [Line Items] |  |  |
Investment owned, balance, shares | 535,265 | 535,265 |
Economic basis per share (in dollars per share) | $ 56.05 |  |
Available-for-sale securities, amortized cost basis | $ 30,000,000 |  |
Fair value | $ 23,166,000 | $ 35,156,000 |
Closing share price (in dollars per share) | $ 43.28 | $ 65.68 |
Change in fair value of marketable securities (see Note 5) | $ (11,990,000) | $ 0 | $ 0
Macerich |  |  |
Marketable Securities [Line Items] |  |  |
Closing share price (in dollars per share) | $ 43.28 | $ 65.68 |
Change in fair value of marketable securities (see Note 5) | $ (11,990,000) |  |

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