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, 2012
Net Lease Strategic Assets Fund L P [Member]
Business Acquisition [Line Items]
Gross revenues	$ 92,035	$ 271,258
Net income (loss) attributable to Lexington Realty Trust shareholders	916	(5,552)
Net loss attributable to common shareholders	$ (3,737)	$ (23,906)
Net loss per common share - basic and diluted	$ (0.02)	$ (0.15)