Investments in Unconsolidated Joint Ventures - Additional Information (Details) $ in Thousands	1 Months Ended			3 Months Ended	12 Months Ended
	Aug. 31, 2020 USD ($)	Jan. 31, 2018 USD ($)	Oct. 31, 2016	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) ft² unit	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
General information on each joint venture
Investments in unconsolidated joint ventures | $					$ 3,823,322	$ 2,912,842
Net equity investment in VIEs in which the entity is not primary beneficiary | $					$ 134,000	145,900
Approximate Square Feet					29,500,737
Purchase price and other fair value adjustment | $					$ 187,522	69,389	$ 57,385
(Loss) gain on sale of real estate, net | $					$ 215,506	$ (16,749)	$ (30,757)
21 East 66th Street | Three Retail and Two Residential Units
General information on each joint venture
Ownership Interest Sold					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 Sold					16.14%
Number of residential units | unit					3
Stonehenge Portfolio
General information on each joint venture
Ownership Interest Sold			90.00%
400 East 57th Street
General information on each joint venture
Ownership Interest Sold			51.00%
1552 Broadway
General information on each joint venture
Approximate Square Feet					13,045
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, ownership percentage					9.60%
126 Nassau Street
General information on each joint venture
(Loss) gain on sale of real estate, net | $	$ 17,700
Joint venture
General information on each joint venture
Investments in unconsolidated joint ventures | $					$ 3,823,322
Equity method investments with negative book value | $					$ 89,600
Joint venture | 100 Park Avenue
General information on each joint venture
Ownership Interest Sold					49.90%
Economic Interest, percent					49.90%
Approximate Square Feet					834,000
Joint venture | 717 Fifth Avenue
General information on each joint venture
Ownership Interest Sold					10.92%
Economic Interest, percent					10.92%
Approximate Square Feet					119,500
Joint venture | 800 Third Avenue
General information on each joint venture
Ownership Interest Sold					60.52%
Economic Interest, percent					60.52%
Approximate Square Feet					526,000
Joint venture | 919 Third Avenue
General information on each joint venture
Ownership Interest Sold					51.00%
Economic Interest, percent					51.00%
Approximate Square Feet					1,454,000
Joint venture | 11 West 34th Street
General information on each joint venture
Ownership Interest Sold					30.00%
Economic Interest, percent					30.00%
Approximate Square Feet					17,150
Joint venture | 280 Park Avenue
General information on each joint venture
Ownership Interest Sold					50.00%
Economic Interest, percent					50.00%
Approximate Square Feet					1,219,158
Joint venture | 1552 Broadway
General information on each joint venture
Ownership Interest Sold					50.00%
Economic Interest, percent					50.00%
Approximate Square Feet					57,718
Joint venture | 10 East 53rd Street
General information on each joint venture
Ownership Interest Sold					55.00%
Economic Interest, percent					55.00%
Approximate Square Feet					354,300
Joint venture | 21 East 66th Street
General information on each joint venture
Ownership Interest Sold					32.28%
Economic Interest, percent					32.28%
Approximate Square Feet					13,069
Joint venture | 650 Fifth Avenue
General information on each joint venture
Ownership Interest Sold					50.00%
Economic Interest, percent					50.00%
Approximate Square Feet					69,214
Joint venture | 121 Greene Street
General information on each joint venture
Ownership Interest Sold					50.00%
Economic Interest, percent					50.00%
Approximate Square Feet					7,131
Joint venture | 55 West 46th Street (5)
General information on each joint venture
Ownership Interest Sold					25.00%
Economic Interest, percent					25.00%
Approximate Square Feet					347,000
Joint venture | 55 West 46th Street (5) | Forecast
General information on each joint venture
(Loss) gain on sale of real estate, net | $				$ (17,800)
Joint venture | Stonehenge Portfolio
General information on each joint venture
Ownership Interest Sold			10.00%
Approximate Square Feet					1,439,016
Joint venture | 605 West 42nd Street
General information on each joint venture
Ownership Interest Sold					20.00%
Economic Interest, percent					20.00%
Approximate Square Feet					927,358
Joint venture | 11 Madison Avenue
General information on each joint venture
Ownership Interest Sold					60.00%
Economic Interest, percent					60.00%
Approximate Square Feet					2,314,000
Joint venture | 400 East 57th Street
General information on each joint venture
Ownership Interest Sold					51.00%
Economic Interest, percent					41.00%
Approximate Square Feet					290,482
Joint venture | One Vanderbilt
General information on each joint venture
Ownership Interest Sold					71.01%
Economic Interest, percent					71.01%
Approximate Square Feet					1,657,198
Joint venture | Worldwide Plaza
General information on each joint venture
Ownership Interest Sold					24.35%
Economic Interest, percent					24.35%
Approximate Square Feet					2,048,725
Joint venture | 1515 Broadway
General information on each joint venture
Ownership Interest Sold					56.87%
Economic Interest, percent					56.87%
Approximate Square Feet					1,750,000
Joint venture | 2 Herald Square
General information on each joint venture
Ownership Interest Sold					51.00%
Economic Interest, percent					51.00%
Approximate Square Feet					369,000
Joint venture | Spring Street 115
General information on each joint venture
Ownership Interest Sold					51.00%
Economic Interest, percent					51.00%
Approximate Square Feet					5,218
Joint venture | 885 Third Avenue
General information on each joint venture
Economic Interest, percent					100.00%
Approximate Square Feet					625,300
Joint venture | 15 Beekman
General information on each joint venture
Ownership Interest Sold					20.00%
Economic Interest, percent					20.00%
Approximate Square Feet					221,884
Joint venture | 85 Fifth Avenue
General information on each joint venture
Ownership Interest Sold					36.30%
Economic Interest, percent					36.30%
Approximate Square Feet					12,946
Joint venture | One Madison Avenue
General information on each joint venture
Ownership Interest Sold					50.50%
Economic Interest, percent					50.50%
Approximate Square Feet					1,048,700
919 Third Avenue
General information on each joint venture
Purchase price and other fair value adjustment | $		$ 49,300
One Madison Avenue
General information on each joint venture
Ownership percentage deconsolidated					50.50%
Investment fair value adjustment | $					$ 187,500
400 East 57th Street
General information on each joint venture
Ownership percentage in disposed asset			49.00%