Deferred Costs, Acquired Lease Intangibles and Goodwill - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Deferred Costs [Line Items]
Amortization expense related to deferred leasing costs and acquired deferred leasing costs	$ 6,200		$ 18,300
Amortization expense related to deferred leasing costs and acquired deferred leasing costs		$ 6,300		$ 18,400
Rental revenue related to the amortization of below-market leases, net of above-market leases	1,700	1,700	5,780	4,387
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	2,400	$ 2,900	8,200	$ 9,300
Unsecured revolving credit facility | Unsecured revolving credit facility
Deferred Costs [Line Items]
Net deferred financing costs	$ 4,700		$ 4,700		$ 6,300