Investments in Real Estate and Real Estate Under Construction - Acquisition, Pro Forma (Details) (Net Lease Strategic Assets Fund L P [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net Lease Strategic Assets Fund L P [Member]
Business Acquisition [Line Items]
Gross revenues	$ 94,940	$ 91,090	$ 279,653	$ 268,836
Net income (loss) attributable to Lexington Realty Trust shareholders	3,969	(39,005)	(1,258)	(117,454)
Net loss attributable to common shareholders	$ (684)	$ (45,139)	$ (19,612)	$ (136,068)
Net loss per common share - basic and diluted	$ 0.00	$ (0.29)	$ (0.13)	$ (0.90)