Mortgages and Other Loans Payable - Schedule of Mortgages and Other Loans Payable (Details) - USD ($) $ in Thousands	Jan. 31, 2026	Dec. 31, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Total fixed rate debt		$ 2,075,222	$ 1,587,474
Total floating rate debt		79,277	363,550
Total mortgages and other loans payable		2,154,499	1,951,024
Deferred financing costs, net of amortization		(8,450)	(6,389)
Total mortgages and other loans payable, net		2,146,049	1,944,635
10 East 53rd Street
Debt Instrument [Line Items]
Total fixed rate debt		204,550	205,000
7 Dey / 185 Broadway
Debt Instrument [Line Items]
Total fixed rate debt		190,149	190,148
100 Church Street
Debt Instrument [Line Items]
Total fixed rate debt		365,000	370,000
Landmark Square
Debt Instrument [Line Items]
Total fixed rate debt		100,000	100,000
315 West 33rd Street
Debt Instrument [Line Items]
Total fixed rate debt		250,000	0
485 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt		450,000	450,000
500 Park Avenue
Debt Instrument [Line Items]
Total fixed rate debt		80,000	0
800 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt		177,000	0
420 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt		258,523	272,326
Debt Fund Subscription Line
Debt Instrument [Line Items]
Total floating rate debt		79,277	0
Maximum facility capacity		100,000
Debt Fund Subscription Line | Subsequent Event
Debt Instrument [Line Items]
Maximum facility capacity	$ 150,000
Fund subscription line ⁽³⁾
Debt Instrument [Line Items]
Total floating rate debt		0	3,550
100 Park Avenue
Debt Instrument [Line Items]
Total floating rate debt		$ 0	$ 360,000
Weighted Average | 10 East 53rd Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)		5.37%
Weighted Average | 7 Dey / 185 Broadway
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 | 315 West 33rd Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)		4.24%
Weighted Average | 485 Lexington Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)		4.25%
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)		3.37%
Weighted Average | 420 Lexington Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)		8.24%
Weighted Average | Debt Fund Subscription Line
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)		2.20%
Weighted Average | Fund subscription line ⁽³⁾
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)		0.00%
Weighted Average | 100 Park Avenue
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)		0.00%