Investments in Partially Owned Entities (Alexander's Inc.) (Details) - Alexanders Inc - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Equity Method Investments And Income From Equity Method Investments
Investment owned, balance, shares	1,654,068
Equity method ownership percentage	32.40%
Amount Alexander owed	$ 1,426	$ 708
Closing share price (in dollars per share)	$ 330.35
Equity method investment, quoted market value	$ 546,421
Excess of investee's fair value over carrying amount	447,878
Excess of investee's carrying amount over equity in net assets	$ 38,838

For an unclassified balance sheet, amount of receivables arising from transactions with related parties.

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