Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Equity Securities	$ 152,927	$ 206,323
Available-for-sale Equity Securities, Amortized Cost Basis	72,549	72,549
Available-for-sale Securities, Gross Unrealized Gain	80,378	133,774
Lexington Realty Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Equity Securities	149,599	202,789
Available-for-sale Equity Securities, Amortized Cost Basis	72,549	72,549
Available-for-sale Securities, Gross Unrealized Gain	77,050	130,240
Other Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Equity Securities	3,328	3,534
Available-for-sale Equity Securities, Amortized Cost Basis	0	0
Available-for-sale Securities, Gross Unrealized Gain	$ 3,328	$ 3,534