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Marketable Securities - Additional Information (Detail) - Macerich Interest [Member] - USD ($) $ / shares in Units, $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Macerich common shares	535,265	535,265
Economic basis per share	$ 56.05
GAAP cost	$ 30,000
Fair value	$ 31,077	$ 37,918
Closing share price	$ 58.06	$ 70.84

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Amount of equity securities categorized neither as held-to-maturity nor as trading.

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Balance held at close of period in number of shares.

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