Deferred Costs, Acquired Lease Intangibles and Goodwill - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Deferred Costs [Line Items]
Amortization of deferred leasing costs	$ 2,600	$ 2,400	$ 5,500	$ 4,800
Amortization of deferred finance costs and debt premiums	1,500	1,400	3,900	2,500
Revenue related to amortization of acquired above- and below-market leases, net	4,600	2,000	9,900	3,900
Goodwill	491,479		491,479		$ 491,479
Lease agreements
Deferred Costs [Line Items]
Amortization expense related to acquired lease intangibles	9,300	$ 5,300	19,600	$ 10,500
Observatory segment
Deferred Costs [Line Items]
Goodwill	227,500		227,500
Real estate segment
Deferred Costs [Line Items]
Goodwill	$ 264,000		$ 264,000