Income per Common Unit of the Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Per Common Unit [Line Items]
Income from continuing operations net of noncontrolling interest																	$ 123,945	$ 115,653	$ 104,522
Preferred Stock Redemption Discount																	3,689
Weighted Average Number of Shares Outstanding, Basic																	116,863,000	114,755,000	112,924,000
Income from continuing operations net of noncontrolling interest, per common unit, basic																	$ 1.06	$ 1.00	$ 0.92
Dilutive units for long-term compensation plans																	831,000	748,000	682,000
Weighted Average Number of Shares Outstanding, Diluted																	117,694,000	115,503,000	113,606,000
Income from Continuing Operations, Per Diluted Common Unit																	$ 1.06	$ 1.00	$ 0.91
Discontinued operations	8,392		(1,845)		3,221		4,153		6,858		5,792		53,854	[1]	4,145		13,921	70,649	23,235
Discontinued operations net of noncontrolling interest, per common unit, basic																	$ 0.12	$ 0.60	$ 0.21
Discontinued operations net of noncontrolling interest, per common unit, diluted																	$ 0.11	$ 0.59	$ 0.21
Net Income Available to Common Shareholders, Basic																	137,436	183,999	127,762
Earnings Per Common Unit, Basic	$ 0.33	[2]	$ 0.24	[2]	$ 0.29	[2]	$ 0.32	[2]	$ 0.30	[2]	$ 0.31	[2]	$ 0.74	[1],[2]	$ 0.25	[2]	$ 1.18	$ 1.60	$ 1.13
Earnings Per Common Unit, Diluted	$ 0.32	[2]	$ 0.24	[2]	$ 0.29	[2]	$ 0.32	[2]	$ 0.30	[2]	$ 0.31	[2]	$ 0.74	[1],[2]	$ 0.25	[2]	$ 1.17	$ 1.59	$ 1.12
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount																	905,000	1,685,000	1,433,000
Stock Issued During Period, Shares, Stock Options Exercised																	841,000	256,000	315,000
Common Units Exchanged																	94,895	119,987	82,621
Common Stock, Dividends, Per Share, Declared																	$ 1.90	$ 1.90	$ 1.90
Liberty Property Limited Partnership [Member]
Income Per Common Unit [Line Items]
Income from continuing operations net of noncontrolling interest																	134,105	140,572	129,975
Less: Preferred unit distributions																	(9,902)	(21,069)	(21,012)
Preferred Stock Redemption Discount																	3,689	0	0
Income from Continuing Operations available to Common Unitholders																	127,892	119,503	108,963
Weighted Average Number of Shares Outstanding, Basic																	120,623,000	118,624,000	116,871,000
Income from continuing operations net of noncontrolling interest, per common unit, basic																	$ 1.06	$ 1.00	$ 0.92
Dilutive units for long-term compensation plans																	831,000	748,000	682,000
Weighted Average Number of Shares Outstanding, Diluted																	121,454,000	119,372,000	117,553,000
Income from Continuing Operations, Per Diluted Common Unit																	$ 1.06	$ 1.00	$ 0.91
Discontinued operations																	13,921	70,649	23,235
Discontinued operations net of noncontrolling interest, per common unit, basic																	$ 0.12	$ 0.60	$ 0.21
Discontinued operations net of noncontrolling interest, per common unit, diluted																	$ 0.11	$ 0.59	$ 0.21
Net Income Available to Common Shareholders, Basic																	$ 141,813	$ 190,152	$ 132,198
Earnings Per Common Unit, Basic																	$ 1.18	$ 1.60	$ 1.13
Earnings Per Common Unit, Diluted																	$ 1.17	$ 1.59	$ 1.12
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount																	905,000	1,685,000	1,433,000
Stock Issued During Period, Shares, Stock Options Exercised																	841,000	256,000	315,000
Common Units Exchanged																		119,987	82,621
Common Stock, Dividends, Per Share, Declared																	$ 1.90	$ 1.90	$ 1.90

[1] Includes gain on sale included in discontinued operations of $50.2 million.

[2] The sum of quarterly financial data may vary from the annual data due to rounding.