Marketable Securities (Marketable securities portfolio) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Available-for-sale Securities
Available-for-sale Securities, Equity Securities	$ 188,695	$ 203,704
Available-for-sale Equity Securities, Amortized Cost Basis	73,199	73,199
Available-for-sale Securities, Gross Unrealized Gain	115,496	130,505
Lexington Realty Trust
Available-for-sale Securities
Available-for-sale Securities, Equity Securities	184,320	199,465
Available-for-sale Equity Securities, Amortized Cost Basis	72,549	72,549
Available-for-sale Securities, Gross Unrealized Gain	111,771	126,916
Other Equity Securities
Available-for-sale Securities
Available-for-sale Securities, Equity Securities	4,375	4,239
Available-for-sale Equity Securities, Amortized Cost Basis	650	650
Available-for-sale Securities, Gross Unrealized Gain	$ 3,725	$ 3,589