Investments in Partially Owned Entities (Alexander's Inc.) (Details)		12 Months Ended
	May 19, 2023 USD ($)	Dec. 31, 2023 USD ($) $ / shares $ / ft² shares	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Schedule of Equity Method Investments [Line Items]
Tenant and other receivables		$ 69,543,000	$ 81,170,000
Alexander's
Schedule of Equity Method Investments [Line Items]
Ownership interest		32.40%
Net realized (loss) income on exited investments		$ 16,396,000	0	$ 14,576,000
Alexander's | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Investment owned, balance (in shares) | shares		1,654,068
Ownership interest		32.40%
Tenant and other receivables		$ 715,000	801,000
Closing share price (in dollars per share) | $ / shares		$ 213.57
Equity method investment fair value		$ 353,259,000
Excess of investee's fair value over carrying amount		265,749,000
Excess of investee's carrying amount over equity in net assets		29,524,000
Management fee income		$ 2,800,000
Development fee percent		6.00%
Lease fee percentage of rent one to ten years		3.00%
Lease fee percentage of rent eleven to twenty years		2.00%
Lease fee percentage of rent twenty first to thirty years		1.00%
Percentage increase lease fee if broker used		1.00%
Percentage commissions on sale of assets under fifty million		3.00%
Asset sale commission threshold		$ 50,000,000
Percentage commissions on sale of assets over fifty million		1.00%
Equity method investment, agreement to sell, amount	$ 71,060,000
Net realized (loss) income on exited investments	16,396,000
Proceeds from commissions received	711,000
Commissions paid to third-party broker	$ 250,000
Alexander's | Equity Method Investee | Fee and other income
Schedule of Equity Method Investments [Line Items]
Fee income recognized by equity method investees for building maintenance services		$ 4,629,000	$ 4,601,000	$ 4,234,000
Alexander's | Equity Method Investee | Rego Park 2 Property
Schedule of Equity Method Investments [Line Items]
Property management fee agreement percentage of income		2.00%
Alexander's | Equity Method Investee | 731 Lexington Avenue
Schedule of Equity Method Investments [Line Items]
Property management fee agreement price per square foot | $ / ft²		0.50
Alexander's | Equity Method Investee | Common Area 731 Lexington Avenue
Schedule of Equity Method Investments [Line Items]
Management fee income		$ 365,000
Property management fee agreement escalation percentage of income		3.00%