Revenue Recognition (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Disaggregation of Revenue [Line Items]
Cumulative effect of accounting change			$ 14,519
Number of reportable segments | segment	2
Base rent (included in property rentals)	$ 406,565	$ 383,843
Property rentals	440,110	414,892
Operating expense reimbursements	47,846	46,401
Tenant services	12,464	12,632
Tenant expense reimbursements	60,310	59,033
BMS cleaning fees	28,355	25,071
Management and leasing fees	2,764	2,275
Lease termination fees	345	3,850
Other income	4,553	2,937
Fee and other income	36,017	34,133
Total revenues	536,437	508,058
Trade Shows
Disaggregation of Revenue [Line Items]
Property rentals	18,873	18,408
Hotel Pennsylvania
Disaggregation of Revenue [Line Items]
Property rentals	14,672	12,641
New York
Disaggregation of Revenue [Line Items]
Base rent (included in property rentals)	344,674	325,681
Property rentals	359,346	338,322
Operating expense reimbursements	44,719	43,005
Tenant services	9,771	10,534
Tenant expense reimbursements	54,490	53,539
BMS cleaning fees	30,153	26,123
Management and leasing fees	2,481	2,027
Lease termination fees	308	3,727
Other income	1,706	2,501
Fee and other income	34,648	34,378
Total revenues	448,484	426,239
New York | Trade Shows
Disaggregation of Revenue [Line Items]
Property rentals	0	0
New York | Hotel Pennsylvania
Disaggregation of Revenue [Line Items]
Property rentals	14,672	12,641
Other
Disaggregation of Revenue [Line Items]
Base rent (included in property rentals)	61,891	58,162
Property rentals	80,764	76,570
Operating expense reimbursements	3,127	3,396
Tenant services	2,693	2,098
Tenant expense reimbursements	5,820	5,494
BMS cleaning fees	(1,798)	(1,052)
Management and leasing fees	283	248
Lease termination fees	37	123
Other income	2,847	436
Fee and other income	1,369	(245)
Total revenues	87,953	81,819
Other | Trade Shows
Disaggregation of Revenue [Line Items]
Property rentals	18,873	18,408
Other | Hotel Pennsylvania
Disaggregation of Revenue [Line Items]
Property rentals	$ 0	$ 0