Revenue Recognition (Revenues by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Lease income	$ 330,944	$ 308,316	$ 663,002	$ 699,534
Total revenues	378,941	343,026	758,918	787,558
Write-off of lease receivables deemed uncollectible	1,569	37,587	5,239	38,631
New York
Disaggregation of Revenue [Line Items]
Total revenues	301,144	270,628	605,115	626,243
Other
Disaggregation of Revenue [Line Items]
Total revenues	77,797	72,398	153,803	161,315
Rental revenues
Disaggregation of Revenue [Line Items]
Total revenues	339,596	315,194	678,913	716,468
Rental revenues | New York
Disaggregation of Revenue [Line Items]
Total revenues	266,881	245,649	533,581	560,382
Rental revenues | Other
Disaggregation of Revenue [Line Items]
Total revenues	72,715	69,545	145,332	156,086
Lease revenues
Disaggregation of Revenue [Line Items]
Lease income	330,944	308,316	663,002	699,534
Lease revenues | New York
Disaggregation of Revenue [Line Items]
Lease income	260,953	241,308	522,644	548,661
Lease revenues | Other
Disaggregation of Revenue [Line Items]
Lease income	69,991	67,008	140,358	150,873
Property rentals
Disaggregation of Revenue [Line Items]
Lease income	330,944	308,316	663,002	679,490
Write-off of lease receivables deemed uncollectible		37,587		38,631
Property rentals | New York
Disaggregation of Revenue [Line Items]
Lease income	260,953	241,308	522,644	539,920
Property rentals | Other
Disaggregation of Revenue [Line Items]
Lease income	69,991	67,008	140,358	139,570
Hotel Pennsylvania
Disaggregation of Revenue [Line Items]
Lease income			0	8,741
Hotel Pennsylvania | New York
Disaggregation of Revenue [Line Items]
Lease income			0	8,741
Hotel Pennsylvania | Other
Disaggregation of Revenue [Line Items]
Lease income			0	0
Tenant services
Disaggregation of Revenue [Line Items]
Revenue	8,652	6,878	15,911	16,934
Tenant services | New York
Disaggregation of Revenue [Line Items]
Revenue	5,928	4,341	10,937	11,721
Tenant services | Other
Disaggregation of Revenue [Line Items]
Revenue	2,724	2,537	4,974	5,213
Fee and other income
Disaggregation of Revenue [Line Items]
Revenue	39,345	27,832	80,005	71,090
Total revenues	39,345	27,832	80,005	71,090
Fee and other income | New York
Disaggregation of Revenue [Line Items]
Revenue	34,263	24,979	71,534	65,861
Fee and other income | Other
Disaggregation of Revenue [Line Items]
Revenue	5,082	2,853	8,471	5,229
BMS cleaning fees
Disaggregation of Revenue [Line Items]
Revenue	28,083	21,115	56,560	53,581
BMS cleaning fees | New York
Disaggregation of Revenue [Line Items]
Revenue	29,600	22,405	59,548	56,834
BMS cleaning fees | Other
Disaggregation of Revenue [Line Items]
Revenue	(1,517)	(1,290)	(2,988)	(3,253)
Management and leasing fees
Disaggregation of Revenue [Line Items]
Revenue	3,073	1,837	8,442	4,704
Management and leasing fees | New York
Disaggregation of Revenue [Line Items]
Revenue	3,088	1,701	8,610	4,575
Management and leasing fees | Other
Disaggregation of Revenue [Line Items]
Revenue	(15)	136	(168)	129
Other income
Disaggregation of Revenue [Line Items]
Revenue	8,189	4,880	15,003	12,805
Other income | New York
Disaggregation of Revenue [Line Items]
Revenue	1,575	873	3,376	4,452
Other income | Other
Disaggregation of Revenue [Line Items]
Revenue	6,614	4,007	11,627	8,353
Trade shows
Disaggregation of Revenue [Line Items]
Lease income	0	0	0	11,303
Trade shows | New York
Disaggregation of Revenue [Line Items]
Lease income	0	0	0	0
Trade shows | Other
Disaggregation of Revenue [Line Items]
Lease income	$ 0	$ 0	$ 0	$ 11,303