Investment in and Advances to Non-Consolidated Entities (Details) (USD $)	1 Months Ended	12 Months Ended						1 Months Ended	12 Months Ended							12 Months Ended				12 Months Ended			12 Months Ended				12 Months Ended
	Jul. 31, 2012	Dec. 31, 2012 Partnerships	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Lexington Reality Advisors Inc [Member]	Dec. 31, 2011 Lexington Reality Advisors Inc [Member]	Dec. 31, 2010 Lexington Reality Advisors Inc [Member]	Apr. 30, 2011 Pemlex LLC [Member] sqft	Dec. 31, 2012 Pemlex LLC [Member]	Dec. 31, 2012 Net Lease Strategic Assets Fund L P [Member]	Dec. 31, 2011 Net Lease Strategic Assets Fund L P [Member]	Dec. 31, 2010 Net Lease Strategic Assets Fund L P [Member]	Dec. 31, 2012 Net Lease Strategic Assets Fund L P [Member] Common Stock [Member]	Dec. 31, 2012 Net Lease Strategic Assets Fund L P [Member] Common Stock [Member] Inland American Real Estate Trust Inc [Member]	Dec. 31, 2012 Net Lease Strategic Assets Fund L P [Member] Preferred Shares [Member]	Dec. 31, 2012 Lex Win Concord [Member]	Dec. 31, 2011 Lex Win Concord [Member]	Dec. 31, 2012 Concord and CDH CDO [Member]	Dec. 31, 2012 LW Sofi LLC [Member]	Dec. 31, 2011 Other Nonconsolidated Entity [Member]	Dec. 31, 2012 Partnership [Member] Maximum [Member]	Dec. 31, 2012 Partnership [Member] Minimum [Member]	Dec. 31, 2012 Palm Beach Gardens, Florida [Member] Joint Venture [Member] sqft Y	Dec. 31, 2012 Humble Texas [Member] Joint Venture [Member] Y	Dec. 31, 2012 Nonrecourse Mortgage [Member] Joint Venture [Member]	Dec. 31, 2012 Mortgages [Member]	Dec. 31, 2012 Mortgages [Member] Partnership [Member]	Jul. 31, 2012 Financial Standby Letter of Credit [Member]
Investments in and Advances to Affiliates [Line Items]
Number of joint ventures formed		2
Square feet of property acquired								210,000															120,000
Investment in joint venture		$ 20,172,000	$ 19,940,000	$ 0				$ 14,180,000															$ 29,750,000
Lease term																							15	17
Co-venture equity ownership percentage													15.00%		100.00%						40.00%	27.00%	36.00%	15.00%
Advances to Affiliate																							12,000,000
Property Purchase Price																								27,750,000
Debt interest rate percentage																									4.70%
Internal rate of return on investment								15.00%
Annual preferred return on investment								9.60%
Income from equity method investment		21,531,000	30,334,000	21,741,000					1,344,000	2,382,000	3,599,000	3,636,000
Proceeds from divestiture of interest in consolidated subsidiaries	13,218,000
Guarantor obligations, contingent letter of credit																												2,500,000
Co-venture equity ownership percentage, by partner														85.00%
Equity recognized in income using hypothetical liquidation										12,902,000	21,572,000	19,468,000
Difference between assets contributed and fair value of initial investment										94,723,000
Equity method investment distributions		7,498,000	11,549,000	3,233,000												885,000	3,954,000
Investment sold, carrying amount																		7,000,000
Equity method investment																			5,760,000	719,000
Number of partnerships		6
Loss on impairment																				1,559,000
Mortgage debt																									15,260,000	11,034,000	32,039,000
Interest rate range, minimum																											5.20%
Interest rate range, maximum																											10.60%
Weighted-average interest rate		5.60%	5.70%																								7.50%
Advisory fees					$ 875,000	$ 804,000	$ 967,000