Deferred Costs, Acquired Lease Intangibles and Goodwill - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Deferred Costs [Line Items]
Unsecured revolving credit facility borrowings	$ 0		$ 35,192,000
Net deferred financing costs	12,907,000		12,910,000
Amortization of deferred leasing costs	5,800,000	$ 5,900,000
Revenue related to amortization of acquired above- and below-market leases, net	4,200,000	5,300,000
Goodwill	491,479,000		491,479,000
Observatory
Deferred Costs [Line Items]
Goodwill	227,500,000
Real Estate
Deferred Costs [Line Items]
Goodwill	264,000,000
Lease agreements
Deferred Costs [Line Items]
Amortization expense related to acquired lease intangibles	7,700,000	$ 10,300,000
Unsecured Revolving Credit Facility | Revolving Credit Facility
Deferred Costs [Line Items]
Unsecured revolving credit facility borrowings	0		$ 40,000,000
Unsecured Revolving Credit Facility | Revolving Credit Facility | Deferred costs, net
Deferred Costs [Line Items]
Net deferred financing costs	$ 4,400,000