Revenue Recognition (Revenues by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Lease income	$ 312,748	$ 414,343	$ 1,012,282	$ 1,310,881
Total revenues	363,962	465,961	1,151,520	1,463,732
Write-off of lease receivables deemed uncollectible			60,766	16,488
New York
Disaggregation of Revenue [Line Items]
Total revenues	293,145	380,568	919,388	1,200,234
Other
Disaggregation of Revenue [Line Items]
Total revenues	70,817	85,393	232,132	263,498
Property rentals
Disaggregation of Revenue [Line Items]
Lease income	312,748	381,740	992,238	1,211,641
Write-off of lease receivables deemed uncollectible	22,135	1,106	60,766	16,488
Property rentals | New York
Disaggregation of Revenue [Line Items]
Lease income	248,328	308,933	788,248	995,661
Property rentals | Other
Disaggregation of Revenue [Line Items]
Lease income	64,420	72,807	203,990	215,980
Hotel Pennsylvania
Disaggregation of Revenue [Line Items]
Lease income	0	24,499	8,741	62,633
Hotel Pennsylvania | New York
Disaggregation of Revenue [Line Items]
Lease income	0	24,499	8,741	62,633
Hotel Pennsylvania | Other
Disaggregation of Revenue [Line Items]
Lease income	0	0	0	0
Trade shows
Disaggregation of Revenue [Line Items]
Lease income	0	8,104	11,303	36,607
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	8,104	11,303	36,607
Lease revenues
Disaggregation of Revenue [Line Items]
Lease income	312,748	414,343	1,012,282	1,310,881
Lease revenues | New York
Disaggregation of Revenue [Line Items]
Lease income	248,328	333,432	796,989	1,058,294
Lease revenues | Other
Disaggregation of Revenue [Line Items]
Lease income	64,420	80,911	215,293	252,587
Tenant services
Disaggregation of Revenue [Line Items]
Revenue	9,505	13,295	26,439	37,933
Tenant services | New York
Disaggregation of Revenue [Line Items]
Revenue	6,589	9,342	18,310	27,904
Tenant services | Other
Disaggregation of Revenue [Line Items]
Revenue	2,916	3,953	8,129	10,029
Rental revenues
Disaggregation of Revenue [Line Items]
Total revenues	322,253	427,638	1,038,721	1,348,814
Rental revenues | New York
Disaggregation of Revenue [Line Items]
Total revenues	254,917	342,774	815,299	1,086,198
Rental revenues | Other
Disaggregation of Revenue [Line Items]
Total revenues	67,336	84,864	223,422	262,616
BMS cleaning fees
Disaggregation of Revenue [Line Items]
Revenue	24,054	30,677	77,635	93,032
BMS cleaning fees | New York
Disaggregation of Revenue [Line Items]
Revenue	25,592	32,787	82,426	99,488
BMS cleaning fees | Other
Disaggregation of Revenue [Line Items]
Revenue	(1,538)	(2,110)	(4,791)	(6,456)
Management and leasing fees
Disaggregation of Revenue [Line Items]
Revenue	11,649	3,326	16,353	10,063
Management and leasing fees | New York
Disaggregation of Revenue [Line Items]
Revenue	11,732	3,746	16,307	10,469
Management and leasing fees | Other
Disaggregation of Revenue [Line Items]
Revenue	(83)	(420)	46	(406)
Other income
Disaggregation of Revenue [Line Items]
Revenue	6,006	4,320	18,811	11,823
Other income | New York
Disaggregation of Revenue [Line Items]
Revenue	904	1,261	5,356	4,079
Other income | Other
Disaggregation of Revenue [Line Items]
Revenue	5,102	3,059	13,455	7,744
Fee and other income
Disaggregation of Revenue [Line Items]
Revenue	41,709	38,323	112,799	114,918
Total revenues	41,709	38,323	112,799	114,918
Fee and other income | New York
Disaggregation of Revenue [Line Items]
Revenue	38,228	37,794	104,089	114,036
Fee and other income | Other
Disaggregation of Revenue [Line Items]
Revenue	$ 3,481	$ 529	$ 8,710	$ 882