Investment in Unconsolidated Joint Venture (Narrative) (Details) - USD ($) $ in Thousands	Oct. 30, 2013	Mar. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint venture		$ 208,558	$ 215,370
Worldwide Plaza
Schedule of Equity Method Investments [Line Items]
Ownership percentage	48.90%
Aggregate cost	$ 220,100
Agreed upon value	1,300,000
Notes payable	$ 875,000	875,000	875,000
Interest rate	4.60%
Purchase option term	38 months
Purchase obligation	$ 1,400,000
Fee for non-exercise of purchase option		25,000
Potential loss on investment		233,600
Difference between carrying amount and underlying equity	$ 260,600
Investments in unconsolidated joint venture		208,558	$ 215,370
Parent Company | Worldwide Plaza
Schedule of Equity Method Investments [Line Items]
Notes payable		$ 427,900