Deferred Costs, Acquired Lease Intangibles and Goodwill - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Deferred Costs [Line Items]
Amortization expense related to deferred leasing costs and acquired deferred leasing costs	$ 6,400	$ 5,900	$ 12,300	$ 12,100
Rental revenue related to the amortization of below-market leases, net of above-market leases	1,400	1,700	2,274	4,098
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	$ 2,600	4,400	$ 5,800
Unsecured revolving credit facility | Unsecured revolving credit facility
Deferred Costs [Line Items]
Net deferred financing costs	$ 3,200		$ 3,200		$ 4,200
Observatory
Deferred Costs [Line Items]
Fair value in excess of carrying value (as a percent)	5.00%		5.00%