Deferred Costs, Acquired Lease Intangibles and Goodwill - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
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	2,354	1,168
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	3,200	$ 3,400
Unsecured revolving credit facility | Unsecured term loan facility
Deferred Costs [Line Items]
Net deferred financing costs	$ 5,700		$ 6,300