Deferred Costs, Acquired Lease Intangibles and Goodwill - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Deferred Costs [Line Items]
Amortization expense related to deferred leasing costs	$ 6,200	$ 6,200
Revenue related to amortization of acquired above- and below-market leases, net	1,168	1,428
Goodwill	491,479		$ 491,479
Observatory
Deferred Costs [Line Items]
Goodwill	227,500
Real estate
Deferred Costs [Line Items]
Goodwill	264,000
Lease agreements
Deferred Costs [Line Items]
Amortization expense related to acquired lease intangibles	3,400	$ 4,400
Unsecured revolving credit facility | Unsecured term loan facility
Deferred Costs [Line Items]
Net deferred financing costs	$ 7,800		$ 8,300