Marketable Securities (Marketable securities portfolio) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale Securities
Available-for-sale Securities, Equity Securities	$ 187,489	$ 203,704
Available-for-sale Equity Securities, Amortized Cost Basis	73,199	73,199
Available-for-sale Securities, Gross Unrealized Gain	114,290	130,505
Lexington Realty Trust
Available-for-sale Securities
Available-for-sale Securities, Equity Securities	183,027	199,465
Available-for-sale Equity Securities, Amortized Cost Basis	72,549	72,549
Available-for-sale Securities, Gross Unrealized Gain	110,478	126,916
Other Equity Securities
Available-for-sale Securities
Available-for-sale Securities, Equity Securities	4,462	4,239
Available-for-sale Equity Securities, Amortized Cost Basis	650	650
Available-for-sale Securities, Gross Unrealized Gain	$ 3,812	$ 3,589