Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
OPERATING REVENUE
Rental	$ 466,984	$ 463,240	$ 453,970
Operating expense reimbursement	200,610	193,761	190,726
Total operating revenue	667,594	657,001	644,696
OPERATING EXPENSE
Rental property	127,266	128,180	122,635
Real estate taxes	77,618	75,489	75,981
General and administrative	59,370	52,747	51,229
Depreciation and amortization	157,349	150,692	148,046
Total operating expenses	421,603	407,108	397,891
Operating income	245,991	249,893	246,805
OTHER INCOME (EXPENSE)
Interest and other income	8,397	9,695	11,069
Debt extinguishment gain	0	0	1,547
Interest expense	(122,018)	(134,384)	(133,997)
Total other income (expense)	(113,621)	(124,689)	(121,381)
Income before gain on property dispositions, income taxes, equity in earnings of unconsolidated joint ventures and impairment charges	132,370	125,204	125,424
Gain on property dispositions	5,025	4,616	1,687
Income taxes	(1,020)	(1,736)	(494)
Equity in earnings of unconsolidated joint ventures	3,496	2,296	2,161
Impairment charges - investment in unconsolidated joint ventures and other	0	(378)	(82,552)
Impairment charges - goodwill	0	0	(15,700)
Income from continuing operations	139,871	130,002	30,526
Discontinued operations (including net gain on property dispositions of $60,582, $6,857 and $17,859 for the years ended December 31, 2011, 2010 and 2009, respectively)	70,839	23,373	48,466
Net income	210,710	153,375	78,992
Noncontrolling interest - operating partnership	(27,222)	(25,448)	(23,125)
Noncontrolling interest - consolidated joint ventures	511	(165)	509
Net income available to common shareholders	183,999	127,762	56,376
Basic:
Income from continuing operations	$ 1.00	$ 0.93	$ 0.09
Income from discontinued operations	$ 0.60	$ 0.20	$ 0.43
Income per common share - basic	$ 1.60	$ 1.13	$ 0.52
Diluted:
Income from continuing operations	$ 1.00	$ 0.92	$ 0.09
Income from discontinued operations	$ 0.59	$ 0.20	$ 0.43
Income per common share - diluted	$ 1.59	$ 1.12	$ 0.52
Distributions per common share	$ 1.900	$ 1.900	$ 1.900
Weighted average number of common shares outstanding
Basic	114,755	112,924	107,550
Diluted	115,503	113,606	108,002
Amounts attributable to common shareholders
Income from continuing operations	115,469	105,172	9,623
Discontinued operations	68,530	22,590	46,753
Net income available to common shareholders	183,999	127,762	56,376
Liberty Property Limited Partnership [Member]
OPERATING REVENUE
Rental	466,984	463,240	453,970
Operating expense reimbursement	200,610	193,761	190,726
Total operating revenue	667,594	657,001	644,696
OPERATING EXPENSE
Rental property	127,266	128,180	122,635
Real estate taxes	77,618	75,489	75,981
General and administrative	59,370	52,747	51,229
Depreciation and amortization	157,349	150,692	148,046
Total operating expenses	421,603	407,108	397,891
Operating income	245,991	249,893	246,805
OTHER INCOME (EXPENSE)
Interest and other income	8,397	9,695	11,069
Debt extinguishment gain	0	0	1,547
Interest expense	(122,018)	(134,384)	(133,997)
Total other income (expense)	(113,621)	(124,689)	(121,381)
Income before gain on property dispositions, income taxes, equity in earnings of unconsolidated joint ventures and impairment charges	132,370	125,204	125,424
Gain on property dispositions	5,025	4,616	1,687
Income taxes	(1,020)	(1,736)	(494)
Equity in earnings of unconsolidated joint ventures	3,496	2,296	2,161
Impairment charges - investment in unconsolidated joint ventures and other	0	(378)	(82,552)
Impairment charges - goodwill	0	0	(15,700)
Income from continuing operations	139,871	130,002	30,526
Discontinued operations (including net gain on property dispositions of $60,582, $6,857 and $17,859 for the years ended December 31, 2011, 2010 and 2009, respectively)	70,839	23,373	48,466
Net income	210,710	153,375	78,992
Noncontrolling interest - consolidated joint ventures	511	(165)	509
Preferred unit distributions	(21,069)	(21,012)	(21,012)
Net income available to common shareholders	190,152	132,198	58,489
Basic:
Income from continuing operations	$ 1.00	$ 0.93	$ 0.09
Income from discontinued operations	$ 0.60	$ 0.20	$ 0.43
Income per common share - basic	$ 1.60	$ 1.13	$ 0.52
Diluted:
Income from continuing operations	$ 1.00	$ 0.92	$ 0.09
Income from discontinued operations	$ 0.59	$ 0.20	$ 0.43
Income per common share - diluted	$ 1.59	$ 1.12	$ 0.52
Distributions per common share	$ 1.900	$ 1.900	$ 1.900
Weighted average number of common shares outstanding
Basic	118,624	116,871	111,568
Diluted	119,372	117,553	112,020
Net Income (Loss) Allocated to General Partners	183,999	127,762	56,376
Net Income (Loss) Allocated to Limited Partners	27,222	25,448	23,125
Amounts attributable to common shareholders
Income from continuing operations	140,382	129,837	31,035
Net income available to common shareholders	$ 190,152	$ 132,198	$ 58,489