Consolidated Statements of Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
OPERATING REVENUE
Rental	$ 478,835	$ 464,053	$ 459,940
Operating expense reimbursement	206,717	199,188	192,069
Total operating revenue	685,552	663,241	652,009
OPERATING EXPENSE
Rental property	133,630	125,761	126,423
Real estate taxes	79,859	76,982	74,772
General and administrative	64,730	59,367	52,747
Depreciation and amortization	165,628	156,242	149,457
Total operating expenses	443,847	418,352	403,399
Operating income	241,705	244,889	248,610
OTHER INCOME (EXPENSE)
Interest and other income	9,289	8,389	9,683
Interest expense	(119,630)	(120,718)	(132,951)
Total other income (expense)	(110,341)	(112,329)	(123,268)
Income before gain on property dispositions, income taxes and equity in (loss) earnings of unconsolidated joint ventures	131,364	132,560	125,342
Gain on property dispositions	4,123	5,025	4,238
Income taxes	(976)	(1,020)	(1,736)
Equity in (loss) earnings of unconsolidated joint ventures	(681)	3,496	2,296
Income from continuing operations	133,830	140,061	130,140
Discontinued operations (including net gain on property dispositions of $11,383, $60,582 and $6,857 for the years ended December 31, 2012, 2011 and 2010, respectively)	13,921	70,649	23,235
Net income	147,751	210,710	153,375
Noncontrolling interest - operating partnership	(10,590)	(27,222)	(25,448)
Noncontrolling interest - consolidated joint ventures	275	511	(165)
Excess of preferred unit carrying amount over redemption	3,689
Net income available to common shareholders	137,436	183,999	127,762
Comprehensive income attributable to common shareholders
Net income	147,751	210,710	153,375
Other comprehensive income (loss) - foreign currency translation	3,436	(280)	(2,582)
Comprehensive income	151,187	210,430	150,793
Less: comprehensive income attributable to noncontrolling interest	(10,422)	(26,706)	(25,525)
Comprehensive income attributable to common shareholders	140,765	183,724	125,268
Basic:
Income from continuing operations	$ 1.06	$ 1.00	$ 0.92
Income from discontinued operations	$ 0.12	$ 0.60	$ 0.21
Income per common share - basic	$ 1.18	$ 1.60	$ 1.13
Diluted:
Income from continuing operations	$ 1.06	$ 1.00	$ 0.91
Income from discontinued operations	$ 0.11	$ 0.59	$ 0.21
Income per common share - diluted	$ 1.17	$ 1.59	$ 1.12
Weighted average number of common shares outstanding
Basic	116,863	114,755	112,924
Diluted	117,694	115,503	113,606
Amounts attributable to common shareholders
Income from continuing operations	123,945	115,653	104,522
Discontinued operations	13,491	68,346	23,240
Net income available to common shareholders	137,436	183,999	127,762
Liberty Property Limited Partnership [Member]
OPERATING REVENUE
Rental	478,835	464,053	459,940
Operating expense reimbursement	206,717	199,188	192,069
Total operating revenue	685,552	663,241	652,009
OPERATING EXPENSE
Rental property	133,630	125,761	126,423
Real estate taxes	79,859	76,982	74,772
General and administrative	64,730	59,367	52,747
Depreciation and amortization	165,628	156,242	149,457
Total operating expenses	443,847	418,352	403,399
Operating income	241,705	244,889	248,610
OTHER INCOME (EXPENSE)
Interest and other income	9,289	8,389	9,683
Interest expense	(119,630)	(120,718)	(132,951)
Total other income (expense)	(110,341)	(112,329)	(123,268)
Income before gain on property dispositions, income taxes and equity in (loss) earnings of unconsolidated joint ventures	131,364	132,560	125,342
Gain on property dispositions	4,123	5,025	4,238
Income taxes	(976)	(1,020)	(1,736)
Equity in (loss) earnings of unconsolidated joint ventures	(681)	3,496	2,296
Income from continuing operations	133,830	140,061	130,140
Discontinued operations (including net gain on property dispositions of $11,383, $60,582 and $6,857 for the years ended December 31, 2012, 2011 and 2010, respectively)	13,921	70,649	23,235
Net income	147,751	210,710	153,375
Noncontrolling interest - consolidated joint ventures	275	511	(165)
Preferred unit distributions	(9,902)	(21,069)	(21,012)
Excess of preferred unit carrying amount over redemption	3,689	0	0
Net income available to common shareholders	141,813	190,152	132,198
Comprehensive income attributable to common shareholders
Net income	147,751	210,710	153,375
Other comprehensive income (loss) - foreign currency translation	3,436	(280)	(2,582)
Comprehensive income	151,187	210,430	150,793
Basic:
Income from continuing operations	$ 1.06	$ 1.00	$ 0.92
Income from discontinued operations	$ 0.12	$ 0.60	$ 0.21
Income per common share - basic	$ 1.18	$ 1.60	$ 1.13
Diluted:
Income from continuing operations	$ 1.06	$ 1.00	$ 0.91
Income from discontinued operations	$ 0.11	$ 0.59	$ 0.21
Income per common share - diluted	$ 1.17	$ 1.59	$ 1.12
Weighted average number of common shares outstanding
Basic	120,623	118,624	116,871
Diluted	121,454	119,372	117,553
Net Income Allocated to General Partners	137,436	183,999	127,762
Net Income Allocated to Limited Partners	10,590	27,222	25,448
Amounts attributable to common shareholders
Income from continuing operations	134,105	140,572	129,975
Net income available to common shareholders	$ 141,813	$ 190,152	$ 132,198