Income per Common Unit of the Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Income Per Common Unit [Line Items]
Income from continuing operations net of noncontrolling interest	$ 29,635	$ 30,021	$ 93,689	$ 88,537
Preferred Stock Redemption Discount			3,689
Weighted Average Number of Shares Outstanding, Basic	117,141,000	115,014,000	116,625,000	114,547,000
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.26	$ 0.26	$ 0.80	$ 0.77
Dilutive units for long-term compensation plans	902,000	766,000	837,000	782,000
Weighted Average Number of Shares Outstanding, Diluted	118,043,000	115,780,000	117,462,000	115,329,000
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.26	$ 0.26	$ 0.79	$ 0.76
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1,887)	5,474	5,487	62,715
(Loss) income from Discontinued Operations, Net of Tax, Per Basic Share	$ (0.02)	$ 0.05	$ 0.05	$ 0.53
(Loss) income from discontinued operations	$ (0.02)	$ 0.05	$ 0.05	$ 0.53
Net Income (Loss) Available to Common Stockholders, Basic	27,806	35,320	99,006	149,207
Earnings Per Share, Basic	$ 0.24	$ 0.31	$ 0.85	$ 1.30
Earnings Per Share, Diluted	$ 0.24	$ 0.31	$ 0.84	$ 1.29
Dilutive Shares, Shares Issued, Shares Acquired on Exchange [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	850,000	1,641,000	905,000	1,219,000
Stock Issued During Period, Shares, Stock Options Exercised	77,000		588,000		256,000
Liberty Property Limited Partnership [Member]
Income Per Common Unit [Line Items]
Income from continuing operations net of noncontrolling interest	31,785	36,260	101,693	107,261
Less: Preferred unit distributions	(1,211)	(5,253)	(8,690)	(15,759)
Preferred Stock Redemption Discount			3,689	0
Income from Continuing Operations available to Common Unitholders	30,574	31,007	96,692	91,502
Weighted Average Number of Shares Outstanding, Basic	120,880,000	118,830,000	120,396,000	118,437,000
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.26	$ 0.26	$ 0.80	$ 0.77
Dilutive units for long-term compensation plans	902,000	766,000	837,000	782,000
Weighted Average Number of Shares Outstanding, Diluted	121,782,000	119,596,000	121,233,000	119,219,000
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.26	$ 0.26	$ 0.79	$ 0.76
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1,887)	5,474	5,487	62,715
(Loss) income from Discontinued Operations, Net of Tax, Per Basic Share	$ (0.02)	$ 0.05	$ 0.05	$ 0.53
(Loss) income from discontinued operations	$ (0.02)	$ 0.05	$ 0.05	$ 0.53
Net Income (Loss) Available to Common Stockholders, Basic	$ 28,687	$ 36,481	$ 102,179	$ 154,217
Earnings Per Share, Basic	$ 0.24	$ 0.31	$ 0.85	$ 1.30
Earnings Per Share, Diluted	$ 0.24	$ 0.31	$ 0.84	$ 1.29
Dilutive Shares, Shares Issued, Shares Acquired on Exchange [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	850,000	1,641,000	905,000	1,219,000
Stock Issued During Period, Shares, Stock Options Exercised	77,000		588,000		256,000