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Marketable Securities - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Investment Holdings [Line Items] |  |
Economic basis per share (in usd per share) | $ 56.05 |
Economic cost | $ 30,000 |
Fair value | $ 16,909 | $ 23,166
Common Stock |  |
Investment Holdings [Line Items] |  |
Macerich common shares (shares) | 535,265 | 535,265
Macerich |  |
Investment Holdings [Line Items] |  |
Closing share price (in usd per share) | $ 31.59 | $ 43.28

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