Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Equity Securities	$ 159,991	$ 206,323
Available-for-sale Equity Securities, Amortized Cost Basis	72,549	72,549
Available-for-sale Securities, Gross Unrealized Gain	87,442	133,774
Lexington Realty Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Equity Securities	156,617	202,789
Available-for-sale Equity Securities, Amortized Cost Basis	72,549	72,549
Available-for-sale Securities, Gross Unrealized Gain	84,068	130,240
Other Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Equity Securities	3,374	3,534
Available-for-sale Equity Securities, Amortized Cost Basis	0	0
Available-for-sale Securities, Gross Unrealized Gain	$ 3,374	$ 3,534