Deferred Costs, Acquired Lease Intangibles and Goodwill - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Deferred Costs [Line Items]
Amortization expense related to deferred leasing costs	$ 5,900	$ 5,900	$ 12,100	$ 12,100
Revenue related to amortization of acquired above- and below-market leases, net	1,700	1,500	4,098	2,719
Goodwill	491,479		491,479		$ 491,479
Observatory
Deferred Costs [Line Items]
Goodwill	227,500		227,500
Real estate
Deferred Costs [Line Items]
Goodwill	264,000		264,000
Lease agreements
Deferred Costs [Line Items]
Amortization expense related to acquired lease intangibles	2,600	$ 3,000	5,800	$ 6,400
Unsecured revolving credit facility | Unsecured term loan facility
Deferred Costs [Line Items]
Net deferred financing costs	$ 5,200		$ 5,200		$ 6,300