Mortgages and Other Loans Payable - Schedule of Mortgages and Other Loans Payable (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Debt Instrument [Line Items]
Total fixed rate debt	$ 2,562,893	$ 2,075,222
Total floating rate debt	136,390	79,277
Total fixed rate and floating rate debt	2,699,283	2,154,499
Mortgages reclassed to liabilities related to assets held for sale	(190,148)	0
Total mortgages and other loans payable	2,509,135	2,154,499
Deferred financing costs, net of amortization	(17,286)	(8,450)
Mortgages and other loans payable, net	2,491,849	2,146,049
10 East 53rd Street
Debt Instrument [Line Items]
Total fixed rate debt	204,438	204,550
7 Dey Street
Debt Instrument [Line Items]
Total fixed rate debt	190,148	190,149
100 Church Street
Debt Instrument [Line Items]
Total fixed rate debt	365,000	365,000
Landmark Square
Debt Instrument [Line Items]
Total fixed rate debt	100,000	100,000
485 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt	450,000	450,000
315 West 33rd Street
Debt Instrument [Line Items]
Total fixed rate debt	250,000	250,000
500 Park Avenue
Debt Instrument [Line Items]
Total fixed rate debt	80,000	80,000
800 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	177,000	177,000
Commercial Condominium at 610 Park Avenue
Debt Instrument [Line Items]
Total fixed rate debt	12,200	0
Park Avenue Tower
Debt Instrument [Line Items]
Total fixed rate debt	480,000	0
800 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	254,107	258,523
Fund subscription line
Debt Instrument [Line Items]
Total floating rate debt	136,390	$ 79,277
Maximum facility capacity	$ 200,000
Weighted Average | 10 East 53rd Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.37%
Weighted Average | 7 Dey Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	6.35%
Weighted Average | 100 Church Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.89%
Weighted Average | Landmark Square
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.90%
Weighted Average | 485 Lexington Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.25%
Weighted Average | 315 West 33rd Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.24%
Weighted Average | 500 Park Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	6.57%
Weighted Average | 800 Third Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.15%
Weighted Average | Commercial Condominium at 610 Park Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.65%
Weighted Average | Park Avenue Tower
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.30%
Weighted Average | 800 Third Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	8.24%
Weighted Average | Fund subscription line
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.20%