Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value	$ 184,154	$ 191,917
Available-for-sale Equity Securities, Amortized Cost Basis	72,606	72,608
Available-for-sale Securities, Gross Unrealized Gain	111,548	119,309
Lexington Realty Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value	180,811	188,567
Available-for-sale Equity Securities, Amortized Cost Basis	72,549	72,549
Available-for-sale Securities, Gross Unrealized Gain	108,262	116,018
Other Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value	3,343	3,350
Available-for-sale Equity Securities, Amortized Cost Basis	57	59
Available-for-sale Securities, Gross Unrealized Gain	$ 3,286	$ 3,291