Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
OPERATING ACTIVITIES
Net income	$ 147,751	$ 210,710	$ 153,375
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	167,421	171,714	174,013
Amortization of deferred financing costs	4,682	5,190	6,339
Equity in loss (earnings) of unconsolidated joint ventures	681	(3,496)	(2,296)
Distributions from unconsolidated joint ventures	624	551	657
Gain on property dispositions	(15,506)	(65,607)	(11,095)
Noncash compensation	10,057	10,555	11,595
Changes in operating assets and liabilities:
Restricted cash	30,713	(14,114)	(7,294)
Accounts receivable	(799)	(1,320)	(850)
Deferred rent receivable	(6,363)	(6,566)	(13,581)
Prepaid expenses and other assets	(10,871)	6,027	(7,597)
Accounts payable	7,641	(229)	(7,399)
Accrued interest	(3,983)	(5,674)	(1,430)
Other liabilities	(14,882)	9,983	(2,173)
Net cash provided by operating activities	317,166	317,724	292,264
INVESTING ACTIVITIES
Investment in properties - acquisitions	(211,894)	(233,568)	(43,505)
Investment in properties - other	(49,682)	(75,834)	(75,857)
Investments in and advances to unconsolidated joint ventures	(1,461)	(11,195)	(1,870)
Distributions from unconsolidated joint ventures	6,009	11,364	6,776
Net proceeds from disposition of properties/land	234,686	390,754	35,934
Net (advances on) proceeds from public reimbursement receivable/escrow	(986)	(10,237)	18,917
Investment in development in progress	(199,384)	(48,628)	(7,481)
Investment in land held for development	(67,513)	(52,868)	(6,086)
Investment in deferred leasing costs	(22,444)	(26,011)	(30,289)
Net cash used in investing activities	(312,669)	(56,223)	(103,461)
FINANCING ACTIVITIES
Net proceeds from issuance of Common Shares	58,710	44,552	37,434
Redemption of preferred units	(221,000)	(9,060)	0
Proceeds from unsecured notes	700,000	0	366,000
Repayments of unsecured notes	(230,100)	(246,500)	(169,739)
Proceeds from mortgage loans	34,599	0	743
Repayments of mortgage loans	(35,099)	(29,860)	(156,890)
Proceeds from credit facility	839,250	650,500	338,500
Repayments on credit facility	(886,650)	(511,100)	(478,500)
Increase in deferred financing costs	(7,206)	(3,023)	(9,697)
Distribution paid on Common Shares	(222,573)	(218,613)	(215,083)
Distribution paid on units	(17,241)	(28,409)	(28,610)
Net cash provided by (used in) financing activities	12,690	(351,513)	(315,842)
Net increase (decrease) in cash and cash equivalents	17,187	(90,012)	(127,039)
Increase (decrease) in cash and cash equivalents related to foreign currency translation	2,965	(193)	(1,998)
Cash and cash equivalents at beginning of year	18,204	108,409	237,446
Cash and cash equivalents at end of year	38,356	18,204	108,409
Liberty Property Limited Partnership [Member]
OPERATING ACTIVITIES
Net income	147,751	210,710	153,375
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	167,421	171,714	174,013
Amortization of deferred financing costs	4,682	5,190	6,339
Equity in loss (earnings) of unconsolidated joint ventures	681	(3,496)	(2,296)
Distributions from unconsolidated joint ventures	624	551	657
Gain on property dispositions	(15,506)	(65,607)	(11,095)
Noncash compensation	10,057	10,555	11,595
Changes in operating assets and liabilities:
Restricted cash	30,713	(14,114)	(7,294)
Accounts receivable	(799)	(1,320)	(850)
Deferred rent receivable	(6,363)	(6,566)	(13,581)
Prepaid expenses and other assets	(10,871)	6,027	(7,597)
Accounts payable	7,641	(229)	(7,399)
Accrued interest	(3,983)	(5,674)	(1,430)
Other liabilities	(14,882)	9,983	(2,173)
Net cash provided by operating activities	317,166	317,724	292,264
INVESTING ACTIVITIES
Investment in properties - acquisitions	(211,894)	(233,568)	(43,505)
Investment in properties - other	(49,682)	(75,834)	(75,857)
Investments in and advances to unconsolidated joint ventures	(1,461)	(11,195)	(1,870)
Distributions from unconsolidated joint ventures	6,009	11,364	6,776
Net proceeds from disposition of properties/land	234,686	390,754	35,934
Net (advances on) proceeds from public reimbursement receivable/escrow	(986)	(10,237)	18,917
Investment in development in progress	(199,384)	(48,628)	(7,481)
Investment in land held for development	(67,513)	(52,868)	(6,086)
Investment in deferred leasing costs	(22,444)	(26,011)	(30,289)
Net cash used in investing activities	(312,669)	(56,223)	(103,461)
FINANCING ACTIVITIES
Redemption of preferred units	(221,000)	(9,060)	0
Proceeds from unsecured notes	700,000	0	366,000
Repayments of unsecured notes	(230,100)	(246,500)	(169,739)
Proceeds from mortgage loans	34,599	0	743
Repayments of mortgage loans	(35,099)	(29,860)	(156,890)
Proceeds from credit facility	839,250	650,500	338,500
Repayments on credit facility	(886,650)	(511,100)	(478,500)
Increase in deferred financing costs	(7,206)	(3,023)	(9,697)
Capital contributions	58,710	44,552	37,434
Distributions to partners	(239,814)	(247,022)	(243,693)
Net cash provided by (used in) financing activities	12,690	(351,513)	(315,842)
Net increase (decrease) in cash and cash equivalents	17,187	(90,012)	(127,039)
Increase (decrease) in cash and cash equivalents related to foreign currency translation	2,965	(193)	(1,998)
Cash and cash equivalents at beginning of year	18,204	108,409	237,446
Cash and cash equivalents at end of year	$ 38,356	$ 18,204	$ 108,409