Revenue Recognition (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)	Jan. 01, 2018 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)	$ 405,927	$ 393,116	$ 812,490	$ 776,956
Property rentals	444,595	428,643	884,705	843,535
Operating expense reimbursements	44,784	39,014	92,652	85,389
Tenant services	13,528	12,643	25,970	25,301
Tenant expense reimbursements	58,312	51,657	118,622	110,690
BMS cleaning fees	30,867	24,425	59,222	49,496
Management and leasing fees	2,707	2,777	5,471	5,052
Lease termination fees	804	1,106	1,149	4,956
Other income	4,533	2,479	9,086	5,416
Fee and other income	38,911	30,787	74,928	64,920
Total revenues	541,818	511,087	1,078,255	1,019,145
Hotel Pennsylvania
Disaggregation of Revenue [Line Items]
Property rentals	27,082	24,986	41,754	37,627
Trade Shows
Disaggregation of Revenue [Line Items]
Property rentals	11,586	10,541	30,461	28,952
New York
Disaggregation of Revenue [Line Items]
Base rent (included in property rentals)	343,084	334,476	687,758	660,157
Property rentals	370,166	359,462	729,512	697,784
Operating expense reimbursements	40,356	35,510	85,082	78,466
Tenant services	10,394	10,031	20,158	20,614
Tenant expense reimbursements	50,750	45,541	105,240	99,080
BMS cleaning fees	33,407	26,617	63,560	52,740
Management and leasing fees	2,464	2,465	4,945	4,492
Lease termination fees	400	1,062	708	4,789
Other income	1,365	1,715	3,071	4,216
Fee and other income	37,636	31,859	72,284	66,237
Total revenues	458,552	436,862	907,036	863,101
New York | Hotel Pennsylvania
Disaggregation of Revenue [Line Items]
Property rentals	27,082	24,986	41,754	37,627
New York | Trade Shows
Disaggregation of Revenue [Line Items]
Property rentals	0	0	0	0
Other
Disaggregation of Revenue [Line Items]
Base rent (included in property rentals)	62,843	58,640	124,732	116,799
Property rentals	74,429	69,181	155,193	145,751
Operating expense reimbursements	4,428	3,504	7,570	6,923
Tenant services	3,134	2,612	5,812	4,687
Tenant expense reimbursements	7,562	6,116	13,382	11,610
BMS cleaning fees	(2,540)	(2,192)	(4,338)	(3,244)
Management and leasing fees	243	312	526	560
Lease termination fees	404	44	441	167
Other income	3,168	764	6,015	1,200
Fee and other income	1,275	(1,072)	2,644	(1,317)
Total revenues	83,266	74,225	171,219	156,044
Other | Hotel Pennsylvania
Disaggregation of Revenue [Line Items]
Property rentals	0	0	0	0
Other | Trade Shows
Disaggregation of Revenue [Line Items]
Property rentals	$ 11,586	$ 10,541	$ 30,461	$ 28,952
Accounting Standards Update 2014-09 | Retained Earnings
Disaggregation of Revenue [Line Items]
Cumulative effect of accounting change					$ 14,519