Investments in Unconsolidated Joint Ventures - Additional Information (Details) $ in Thousands	1 Months Ended	9 Months Ended	12 Months Ended
	May 31, 2021	Sep. 30, 2021 USD ($) ft² unit partner	Dec. 31, 2020 USD ($)	Jul. 31, 2021 ft²
General information on each joint venture
Equity method investments | $		$ 3,028,084	$ 3,823,322
Net equity investment in VIEs in which the entity is not primary beneficiary | $		$ 87,400	$ 134,000
Unaudited Approximate Square Feet (sqft)		28,035,572
One Madison Avenue
General information on each joint venture
Ownership percentage deconsolidated			50.50%
Investment fair value adjustment | $		$ 2,700	$ 187,500
Worldwide Plaza
General information on each joint venture
Ownership percentage acquired	1.20%
Increase in ownership interest	0.60%
One Madison Avenue
General information on each joint venture
Investment in joint venture aggregate equity committed by partner | $			$ 492,200
Investment in joint venture aggregate maximum ownership percentage			49.50%
Investment in joint venture, number of partners | partner		2
Investment in joint venture, ownership percentage		9.00%
220 East 42nd Street | 220 East 42nd Street
General information on each joint venture
Ownership percentage deconsolidated				51.00%
Investment fair value adjustment | $		$ 206,800
220 East 42nd Street
General information on each joint venture
Unaudited Approximate Square Feet (sqft)				1,135,000
Ownership interest disposed				49.00%
21 East 66th Street | Three Retail and Two Residential Units
General information on each joint venture
Ownership interest		32.28%
Number of stores | unit		3
Number of residential units | unit		1
21 East 66th Street | Three Residential Units
General information on each joint venture
Ownership interest		16.14%
Number of residential units | unit		2
Joint venture
General information on each joint venture
Equity method investments | $		$ 3,028,084
Equity method investments with negative book value | $		$ 100,200
Joint venture | 100 Park Avenue
General information on each joint venture
Ownership interest		49.90%
Economic Interest (as a percent)		49.90%
Unaudited Approximate Square Feet (sqft)		834,000
Joint venture | 717 Fifth Avenue
General information on each joint venture
Ownership interest		10.92%
Economic Interest (as a percent)		10.92%
Unaudited Approximate Square Feet (sqft)		119,500
Joint venture | 800 Third Avenue
General information on each joint venture
Ownership interest		60.52%
Economic Interest (as a percent)		60.52%
Unaudited Approximate Square Feet (sqft)		526,000
Joint venture | 919 Third Avenue
General information on each joint venture
Ownership interest		51.00%
Economic Interest (as a percent)		51.00%
Unaudited Approximate Square Feet (sqft)		1,454,000
Joint venture | 11 West 34th Street
General information on each joint venture
Ownership interest		30.00%
Economic Interest (as a percent)		30.00%
Unaudited Approximate Square Feet (sqft)		17,150
Joint venture | 280 Park Avenue
General information on each joint venture
Ownership interest		50.00%
Economic Interest (as a percent)		50.00%
Unaudited Approximate Square Feet (sqft)		1,219,158
Joint venture | 1552-1560 Broadway
General information on each joint venture
Ownership interest		50.00%
Economic Interest (as a percent)		50.00%
Unaudited Approximate Square Feet (sqft)		57,718
Joint venture | 10 East 53rd Street
General information on each joint venture
Ownership interest		55.00%
Economic Interest (as a percent)		55.00%
Unaudited Approximate Square Feet (sqft)		354,300
Joint venture | 21 East 66th Street
General information on each joint venture
Ownership interest		32.28%
Economic Interest (as a percent)		32.28%
Unaudited Approximate Square Feet (sqft)		13,069
Joint venture | 650 Fifth Avenue
General information on each joint venture
Ownership interest		50.00%
Economic Interest (as a percent)		50.00%
Unaudited Approximate Square Feet (sqft)		69,214
Joint venture | 121 Greene Street
General information on each joint venture
Ownership interest		50.00%
Economic Interest (as a percent)		50.00%
Unaudited Approximate Square Feet (sqft)		7,131
Joint venture | Stonehenge Portfolio
General information on each joint venture
Unaudited Approximate Square Feet (sqft)		1,439,016
Joint venture | 11 Madison Avenue
General information on each joint venture
Ownership interest		60.00%
Economic Interest (as a percent)		60.00%
Unaudited Approximate Square Feet (sqft)		2,314,000
Joint venture | One Vanderbilt
General information on each joint venture
Ownership interest		71.01%
Economic Interest (as a percent)		71.01%
Unaudited Approximate Square Feet (sqft)		1,657,198
Joint venture | Worldwide Plaza
General information on each joint venture
Ownership interest		24.95%
Economic Interest (as a percent)		24.95%
Unaudited Approximate Square Feet (sqft)		2,048,725
Joint venture | 1515 Broadway
General information on each joint venture
Ownership interest		56.87%
Economic Interest (as a percent)		56.87%
Unaudited Approximate Square Feet (sqft)		1,750,000
Joint venture | 2 Herald Square
General information on each joint venture
Ownership interest		51.00%
Economic Interest (as a percent)		51.00%
Unaudited Approximate Square Feet (sqft)		369,000
Joint venture | 115 Spring Street
General information on each joint venture
Ownership interest		51.00%
Economic Interest (as a percent)		51.00%
Unaudited Approximate Square Feet (sqft)		5,218
Joint venture | 15 Beekman
General information on each joint venture
Ownership interest		20.00%
Economic Interest (as a percent)		20.00%
Unaudited Approximate Square Feet (sqft)		221,884
Joint venture | 85 Fifth Avenue
General information on each joint venture
Ownership interest		36.30%
Economic Interest (as a percent)		36.30%
Unaudited Approximate Square Feet (sqft)		12,946
Joint venture | One Madison Avenue
General information on each joint venture
Ownership interest		50.50%
Economic Interest (as a percent)		50.50%
Unaudited Approximate Square Feet (sqft)		1,048,700
Joint venture | 220 East 42nd Street
General information on each joint venture
Ownership interest		51.00%
Economic Interest (as a percent)		51.00%
Unaudited Approximate Square Feet (sqft)		1,135,000
Joint venture | East 400 Street 57
General information on each joint venture
Ownership interest		41.00%