Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value	$ 206,917	$ 191,917
Available-for-sale Equity Securities, Amortized Cost Basis	72,605	72,608
Available-for-sale Securities, Gross Unrealized Gain	134,312	119,309
Lexington Realty Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value	203,344	188,567
Available-for-sale Equity Securities, Amortized Cost Basis	72,549	72,549
Available-for-sale Securities, Gross Unrealized Gain	130,795	116,018
Other Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Fair value	3,573	3,350
Available-for-sale Equity Securities, Amortized Cost Basis	56	59
Available-for-sale Securities, Gross Unrealized Gain	$ 3,517	$ 3,291