Debt - Long-Term Debt (Details) - USD ($)	6 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Outstanding borrowings	$ 0	$ 0
Total principal	2,300,131,000
Deferred financing costs, net	(19,338,000)	(22,112,000)
Mortgages, senior notes, and unsecured term loan facilities, not including unsecured revolving credit facility
Debt Instrument [Line Items]
Total principal	2,300,131,000	2,333,793,000
Deferred financing costs, net	(13,277,000)	(14,881,000)
Unamortized debt discount	(8,135,000)	(8,547,000)
Total	2,278,719,000	2,310,365,000
Metro Center | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 83,824,000	85,032,000
Stated Rate (as a percent)	3.59%
Effective Rate (as a percent)	3.67%
10 Union Square | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 50,000,000	50,000,000
Stated Rate (as a percent)	3.70%
Effective Rate (as a percent)	3.97%
1542 Third Avenue | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 30,000,000	30,000,000
Stated Rate (as a percent)	4.29%
Effective Rate (as a percent)	4.53%
First Stamford Place | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 180,000,000	180,000,000
Stated Rate (as a percent)	4.28%
Effective Rate (as a percent)	4.73%
First Stamford Place - First Lien | Fixed rate mortgage debt
Debt Instrument [Line Items]
Stated Rate (as a percent)	4.09%
Face amount of debt instrument	$ 164,000,000
First Stamford Place - Second Lien | Fixed rate mortgage debt
Debt Instrument [Line Items]
Stated Rate (as a percent)	6.25%
Face amount of debt instrument	$ 16,000,000
1010 Third Avenue and 77 West 55th Street | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 36,255,000	36,670,000
Stated Rate (as a percent)	4.01%
Effective Rate (as a percent)	4.21%
250 West 57th Street | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 180,000,000	180,000,000
Stated Rate (as a percent)	2.83%
Effective Rate (as a percent)	3.21%
10 Bank Street | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 30,609,000	31,091,000
Stated Rate (as a percent)	4.23%
Effective Rate (as a percent)	4.37%
383 Main Avenue | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 0	30,000,000
Stated Rate (as a percent)	0.00%
Effective Rate (as a percent)	0.00%
1333 Broadway | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 160,000,000	160,000,000
Stated Rate (as a percent)	4.21%
Effective Rate (as a percent)	4.29%
345 East 94th Street - Series A | Revolving credit facility | LIBOR
Debt Instrument [Line Items]
Variable rate, effective percentage (as a percent)	70.00%
Basis spread on variable rate (as a percent)	0.95%
345 East 94th Street - Series A | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 43,600,000	43,600,000
Effective Rate (as a percent)	3.56%
345 East 94th Street - Series B | Revolving credit facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.24%
345 East 94th Street - Series B | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 8,173,000	8,650,000
Effective Rate (as a percent)	3.56%
561 10th Avenue - Series A | Revolving credit facility | LIBOR
Debt Instrument [Line Items]
Variable rate, effective percentage (as a percent)	70.00%
Basis spread on variable rate (as a percent)	1.07%
561 10th Avenue - Series A | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 114,500,000	114,500,000
Effective Rate (as a percent)	3.85%
561 10th Avenue - Series B | Revolving credit facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.45%
561 10th Avenue - Series B | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 18,170,000	19,250,000
Effective Rate (as a percent)	3.85%
Total mortgage debt | Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate mortgage debt	$ 935,131,000	968,793,000
Series A | Senior unsecured notes
Debt Instrument [Line Items]
Total	$ 100,000,000	100,000,000
Stated Rate (as a percent)	3.93%
Effective Rate (as a percent)	3.96%
Series B | Senior unsecured notes
Debt Instrument [Line Items]
Total	$ 125,000,000	125,000,000
Stated Rate (as a percent)	4.09%
Effective Rate (as a percent)	4.12%
Series C | Senior unsecured notes
Debt Instrument [Line Items]
Total	$ 125,000,000	125,000,000
Stated Rate (as a percent)	4.18%
Effective Rate (as a percent)	4.21%
Series D | Senior unsecured notes
Debt Instrument [Line Items]
Total	$ 115,000,000	115,000,000
Stated Rate (as a percent)	4.08%
Effective Rate (as a percent)	4.11%
Series E | Senior unsecured notes
Debt Instrument [Line Items]
Total	$ 160,000,000	160,000,000
Stated Rate (as a percent)	4.26%
Effective Rate (as a percent)	4.27%
Series F | Senior unsecured notes
Debt Instrument [Line Items]
Total	$ 175,000,000	175,000,000
Stated Rate (as a percent)	4.44%
Effective Rate (as a percent)	4.45%
Series G | Senior unsecured notes
Debt Instrument [Line Items]
Total	$ 100,000,000	100,000,000
Stated Rate (as a percent)	3.61%
Effective Rate (as a percent)	4.89%
Series H | Senior unsecured notes
Debt Instrument [Line Items]
Total	$ 75,000,000	75,000,000
Stated Rate (as a percent)	3.73%
Effective Rate (as a percent)	5.00%
Unsecured term loan facilities | Revolving credit facility
Debt Instrument [Line Items]
Outstanding borrowings	$ 215,000,000	215,000,000
Effective Rate (as a percent)	3.58%
Unsecured term loan facilities | Revolving credit facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.20%
Unsecured revolving credit facility | Revolving credit facility
Debt Instrument [Line Items]
Outstanding borrowings	$ 0	0
Effective Rate (as a percent)	0.00%
Unsecured revolving credit facility | Revolving credit facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.30%
Unsecured term loan facility | Revolving credit facility
Debt Instrument [Line Items]
Outstanding borrowings	$ 175,000,000	$ 175,000,000
Effective Rate (as a percent)	4.02%
Unsecured term loan facility | Revolving credit facility | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.50%