Deferred Costs, Acquired Lease Intangibles and Goodwill - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Deferred Costs [Line Items]
Amortization of deferred leasing costs	$ 4,100	$ 2,200	$ 9,600	$ 7,000
Amortization of deferred finance costs and debt premiums	1,100	2,700	5,000	5,100
Revenue related to amortization of acquired above- and below-market leases, net	4,800	4,600	14,700	8,500
Goodwill	491,479		491,479		$ 491,479
Observatory segment
Deferred Costs [Line Items]
Goodwill	227,500		227,500
Real estate segment
Deferred Costs [Line Items]
Goodwill	264,000		264,000
Lease agreements
Deferred Costs [Line Items]
Amortization expense related to acquired lease intangibles	$ 9,800	$ 10,100	$ 29,400	$ 20,700