Liberty Property Trust (LPT) 10-Q 3 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information Document - shares	9 Months Ended
	Sep. 30, 2017	Nov. 02, 2017
Entity Information [Line Items]
Entity Registrant Name	LIBERTY PROPERTY TRUST
Entity Central Index Key	921,112
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		147,418,013
Liberty Property Limited Partnership [Member]
Entity Information [Line Items]
Entity Registrant Name	LIBERTY PROPERTY LIMITED PARTNERSHIP
Entity Central Index Key	921,113

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Real Estate [Abstract]
Land and land improvements	$ 1,081,447	$ 1,094,470
Building and improvements	4,539,552	4,501,921
Less accumulated depreciation	(1,015,786)	(940,115)
Operating real estate	4,605,213	4,656,276
Development in progress	395,089	267,450
Land held for development	331,340	336,569
Net real estate	5,331,642	5,260,295
Cash and cash equivalents	47,666	43,642
Restricted cash	16,824	12,383
Accounts receivable	13,258	13,994
Deferred rent receivable	123,718	109,245
Deferred financing and leasing costs, net of accumulated amortization (September 30, 2017, $168,173; December 31, 2016, $152,309)	154,147	153,393
Investments in and advances to unconsolidated joint ventures	283,803	245,078
Assets held for sale	177,549	4,548
Prepaid expenses and other assets	161,067	150,235
Total assets	6,309,674	5,992,813
LIABILITIES
Mortgage loans	269,380	276,650
Unsecured notes	2,282,828	2,280,286
Credit facility	295,000	0
Accounts payable	78,384	65,914
Accrued interest	34,707	21,878
Dividend and distributions payable	60,131	71,501
Other liabilities	209,710	206,124
Total liabilities	3,230,140	2,922,353
Noncontrolling interest - operating partnership - 301,483 preferred units outstanding as of September 30, 2017 and December 31, 2016	7,537	7,537
EQUITY
Common shares of beneficial interest, $.001 par value, 283,987,000 shares authorized; 147,399,264 and 146,993,018 shares issued and outstanding as of September 30, 2017 and December 31, 2016, respectively	147	147
Additional paid-in capital	3,671,758	3,655,910
Accumulated other comprehensive loss	(39,741)	(56,031)
Distributions in excess of net income	(619,350)	(596,635)
Total Liberty Property Trust shareholders' equity	3,012,814	3,003,391
Noncontrolling interest - operating partnership
Noncontrolling interest - operating partnerships	54,525	54,631
Noncontrolling interest - consolidated joint ventures	4,658	4,901
Total owners' equity	3,071,997	3,062,923
Total liabilities, noncontrolling interest - operating partnership and equity	6,309,674	5,992,813
Liberty Property Limited Partnership [Member]
Real Estate [Abstract]
Land and land improvements	1,081,447	1,094,470
Building and improvements	4,539,552	4,501,921
Less accumulated depreciation	(1,015,786)	(940,115)
Operating real estate	4,605,213	4,656,276
Development in progress	395,089	267,450
Land held for development	331,340	336,569
Net real estate	5,331,642	5,260,295
Cash and cash equivalents	47,666	43,642
Restricted cash	16,824	12,383
Accounts receivable	13,258	13,994
Deferred rent receivable	123,718	109,245
Deferred financing and leasing costs, net of accumulated amortization (September 30, 2017, $168,173; December 31, 2016, $152,309)	154,147	153,393
Investments in and advances to unconsolidated joint ventures	283,803	245,078
Assets held for sale	177,549	4,548
Prepaid expenses and other assets	161,067	150,235
Total assets	6,309,674	5,992,813
LIABILITIES
Mortgage loans	269,380	276,650
Unsecured notes	2,282,828	2,280,286
Credit facility	295,000	0
Accounts payable	78,384	65,914
Accrued interest	34,707	21,878
Dividend and distributions payable	60,131	71,501
Other liabilities	209,710	206,124
Total liabilities	3,230,140	2,922,353
Noncontrolling interest - operating partnership - 301,483 preferred units outstanding as of September 30, 2017 and December 31, 2016	7,537	7,537
EQUITY
General partner’s equity - 147,399,264 and 146,993,018 common units outstanding as of September 30, 2017 and December 31, 2016, respectively	3,012,814	3,003,391
Limited partners' equity	54,525	54,631
Noncontrolling interest - operating partnership
Noncontrolling interest - consolidated joint ventures	4,658	4,901
Total owners' equity	3,071,997	3,062,923
Total liabilities, noncontrolling interest - operating partnership and equity	$ 6,309,674	$ 5,992,813

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Deferred financing and leasing costs, accumulated amortization	$ 168,173,000	$ 152,309,000
Limited Partners' common units outstanding	3,528,281	3,530,031
Common shares of beneficial interest, par value per share	$ 0.001	$ 0.001
Common shares of beneficial interest, shares authorized	283,987,000	283,987,000
Common shares of beneficial interest, shares issued	147,399,264	146,993,018
Common shares of beneficial interest, shares outstanding	147,399,264	146,993,018
Liberty Property Limited Partnership [Member]
Deferred financing and leasing costs, accumulated amortization	$ 168,173,000	$ 152,309,000
Limited Partners' common units outstanding	3,528,281	3,530,031
Common shares of beneficial interest, shares outstanding	147,399,264	146,993,018
Series I 2 [Member]
Noncontrolling interest - operating partnership, preferred units outstanding	301,483	301,483
Series I 2 [Member] | Liberty Property Limited Partnership [Member]
Noncontrolling interest - operating partnership, preferred units outstanding	301,483	301,483

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
OPERATING REVENUE
Rental	$ 129,356,000	$ 140,697,000	$ 377,706,000	$ 418,896,000
Operating expense reimbursement	40,121,000	50,160,000	120,523,000	148,757,000
Development service fee income	24,176,000	0	53,920,000	0
Total operating revenue	193,653,000	190,857,000	552,149,000	567,653,000
OPERATING EXPENSE
Rental property	18,941,000	26,496,000	56,541,000	79,752,000
Real estate taxes	23,258,000	25,968,000	69,783,000	76,490,000
General and administrative	11,910,000	15,379,000	43,949,000	51,888,000
Expensed pursuit costs	4,772,000	772,000	4,957,000	882,000
Depreciation and amortization	46,582,000	46,920,000	137,831,000	154,543,000
Development service fee expense	23,665,000	0	52,497,000	0
Impairment charges - real estate assets	9,650,000	0	9,650,000	0
Total operating expenses	138,778,000	115,535,000	375,208,000	363,555,000
Operating income	54,875,000	75,322,000	176,941,000	204,098,000
OTHER INCOME (EXPENSE)
Interest and other income	1,781,000	3,153,000	5,585,000	12,743,000
Loss on debt extinguishment	0	(3,494,000)	0	(3,494,000)
Interest expense	(23,060,000)	(29,528,000)	(67,345,000)	(91,071,000)
Total other income (expense)	(21,279,000)	(29,869,000)	(61,760,000)	(81,822,000)
Income before gain on property dispositions, income taxes and equity in earnings of unconsolidated joint ventures	33,596,000	45,453,000	115,181,000	122,276,000
Gain on property dispositions	23,840,000	1,318,000	30,542,000	25,671,000
Income taxes	(582,000)	(80,000)	(1,528,000)	(1,633,000)
Equity in earnings of unconsolidated joint ventures	4,305,000	9,043,000	14,026,000	19,540,000
Income from continuing operations	61,159,000	55,734,000	158,221,000	165,854,000
Net income	61,159,000	55,734,000	158,221,000	165,854,000
Noncontrolling interest – operating partnership	(1,545,000)	(1,424,000)	(4,044,000)	(4,250,000)
Noncontrolling interest - consolidated joint ventures	(75,000)	(57,000)	(195,000)	(170,000)
Net income available to common shareholders	59,539,000	54,253,000	153,982,000	161,434,000
Comprehensive income attributable to common shareholders
Net income	61,159,000	55,734,000	158,221,000	165,854,000
Other comprehensive income (loss) - foreign currency translation	5,634,000	(4,407,000)	16,314,000	(23,003,000)
Other comprehensive income (loss) - derivative instruments	91,000	663,000	366,000	(1,132,000)
Other comprehensive income (loss)	5,725,000	(3,744,000)	16,680,000	(24,135,000)
Total comprehensive income	66,884,000	51,990,000	174,901,000	141,719,000
Less: comprehensive income attributable to noncontrolling interest	(1,754,000)	(1,393,000)	(4,629,000)	(3,851,000)
Comprehensive income attributable to common shareholders	$ 65,130,000	$ 50,597,000	$ 170,272,000	$ 137,868,000
Weighted average number of common shares outstanding
Basic	146,811	146,215	146,678	146,121
Diluted	147,596	147,107	147,430	146,788
Amounts attributable to common shareholders
Net income available to common shareholders	$ 59,539,000	$ 54,253,000	$ 153,982,000	$ 161,434,000
Liberty Property Limited Partnership [Member]
OPERATING REVENUE
Rental	129,356,000	140,697,000	377,706,000	418,896,000
Operating expense reimbursement	40,121,000	50,160,000	120,523,000	148,757,000
Development service fee income	24,176,000	0	53,920,000	0
Total operating revenue	193,653,000	190,857,000	552,149,000	567,653,000
OPERATING EXPENSE
Rental property	18,941,000	26,496,000	56,541,000	79,752,000
Real estate taxes	23,258,000	25,968,000	69,783,000	76,490,000
General and administrative	11,910,000	15,379,000	43,949,000	51,888,000
Expensed pursuit costs	4,772,000	772,000	4,957,000	882,000
Depreciation and amortization	46,582,000	46,920,000	137,831,000	154,543,000
Development service fee expense	23,665,000	0	52,497,000	0
Impairment charges - real estate assets	9,650,000	0	9,650,000	0
Total operating expenses	138,778,000	115,535,000	375,208,000	363,555,000
Operating income	54,875,000	75,322,000	176,941,000	204,098,000
OTHER INCOME (EXPENSE)
Interest and other income	1,781,000	3,153,000	5,585,000	12,743,000
Loss on debt extinguishment	0	(3,494,000)	0	(3,494,000)
Interest expense	(23,060,000)	(29,528,000)	(67,345,000)	(91,071,000)
Total other income (expense)	(21,279,000)	(29,869,000)	(61,760,000)	(81,822,000)
Income before gain on property dispositions, income taxes and equity in earnings of unconsolidated joint ventures	33,596,000	45,453,000	115,181,000	122,276,000
Gain on property dispositions	23,840,000	1,318,000	30,542,000	25,671,000
Income taxes	(582,000)	(80,000)	(1,528,000)	(1,633,000)
Equity in earnings of unconsolidated joint ventures	4,305,000	9,043,000	14,026,000	19,540,000
Net income	61,159,000	55,734,000	158,221,000	165,854,000
Noncontrolling interest - consolidated joint ventures	(75,000)	(57,000)	(195,000)	(170,000)
Preferred unit distributions	(118,000)	(118,000)	(354,000)	(354,000)
Net income available to common shareholders	60,966,000	55,559,000	157,672,000	165,330,000
Comprehensive income attributable to common shareholders
Net income	61,159,000	55,734,000	158,221,000	165,854,000
Other comprehensive income (loss) - foreign currency translation	5,634,000	(4,407,000)	16,314,000	(23,003,000)
Other comprehensive income (loss) - derivative instruments	91,000	663,000	366,000	(1,132,000)
Other comprehensive income (loss)	5,725,000	(3,744,000)	16,680,000	(24,135,000)
Total comprehensive income	$ 66,884,000	$ 51,990,000	$ 174,901,000	$ 141,719,000
Weighted average number of common shares outstanding
Basic	150,339	149,751	150,206	149,659
Diluted	151,124	150,643	150,958	150,326
Net income allocated to general partners	$ 59,539,000	$ 54,253,000	$ 153,982,000	$ 161,434,000
Net income allocated to limited partners	1,545,000	1,424,000	4,044,000	4,250,000
Amounts attributable to common shareholders
Income from continuing operations	61,084,000	55,677,000	158,026,000	165,684,000
Net income available to common shareholders	$ 60,966,000	$ 55,559,000	$ 157,672,000	$ 165,330,000
Common shares [Member]
Basic:
Income per common share - basic	$ 0.41	$ 0.37	$ 1.05	$ 1.10
Diluted:
Income per common share - diluted	0.40	0.37	1.04	1.10
Distributions per common share or unit	0.40	0.475	1.20	1.425
Common Units [Member] | Liberty Property Limited Partnership [Member]
Basic:
Income per common share - basic	0.41	0.37	1.05	1.10
Diluted:
Income per common share - diluted	0.40	0.37	1.04	1.10
Distributions per common share or unit	$ 0.40	$ 0.475	$ 1.20	$ 1.425

Consolidated Statement of Equit

Consolidated Statement of Equity - USD ($)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Accumulated Distributions in Excess of Net Income [Member]	Parent [Member]	Noncontrolling interest operating partnership Common [Member]	Noncontrolling interest-consolidated joint ventures [Member]	Liberty Property Limited Partnership [Member]	Liberty Property Limited Partnership [Member]General Partner [Member]	Liberty Property Limited Partnership [Member]Limited Partner [Member]	Liberty Property Limited Partnership [Member]Noncontrolling interest-consolidated joint ventures [Member]	Common shares [Member]	Common Units [Member]Liberty Property Limited Partnership [Member]General Partner [Member]	Common Units [Member]Liberty Property Limited Partnership [Member]Limited Partner [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income - foreign currency translation	$ (23,003,000)								$ (23,003,000)
Other comprehensive income - derivative instruments	(1,132,000)								(1,132,000)
Beginning Balance at Dec. 31, 2016	$ 3,062,923,000	$ 147,000	$ 3,655,910,000	$ (56,031,000)	$ (596,635,000)	$ 3,003,391,000	$ 54,631,000	$ 4,901,000	$ 3,062,923,000	$ 3,003,391,000	$ 54,631,000	$ 4,901,000
Common shares outstanding - Beginning Balance (shares) at Dec. 31, 2016	146,993,018								146,993,018				146,993,018
General Partner's units outstanding - Beginning Balance (units) at Dec. 31, 2016														146,993,018
Limited Partners' units outstanding - Beginning Balance (units) at Dec. 31, 2016	3,530,031								3,530,031						3,530,031
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net proceeds from the issuance of common shares	$ 7,356,000		7,356,000			7,356,000
Net proceeds from issuance of common shares (shares)													404,496
Net income	157,867,000				153,982,000	153,982,000	3,690,000	195,000	$ 157,867,000	153,982,000	3,690,000	195,000
Contributions from partners									15,821,000	15,821,000
Contributions from partners (units)														404,496
Distributions	(181,294,000)				(176,697,000)	(176,697,000)	(4,159,000)	(438,000)
Distributions to partners									(181,294,000)	(176,697,000)	(4,159,000)	(438,000)
Share-based compensation	8,465,000		8,465,000			8,465,000
Other comprehensive income - foreign currency translation	16,314,000			15,932,000		15,932,000	382,000		16,314,000	15,932,000	382,000
Other comprehensive income - derivative instruments	366,000			358,000		358,000	8,000		$ 366,000	358,000	8,000
Redemption of noncontrolling interests	$ 0		27,000			27,000	(27,000)
Redemption of limited partners common units for common shares - common units (shares)													1,750	1,750
Redemption of limited partners common units for common shares - common units										(27,000)	27,000
Partners' Capital Account, Units, Converted															(1,750)
Common shares outstanding - Ending Balance (shares) at Sep. 30, 2017	147,399,264								147,399,264				147,399,264
General Partner's units outstanding - Ending Balance (units) at Sep. 30, 2017														147,399,264
Limited Partners' units outstanding - Ending Balance (units) at Sep. 30, 2017	3,528,281								3,528,281						3,528,281
Ending Balance at Sep. 30, 2017	$ 3,071,997,000	$ 147,000	$ 3,671,758,000	$ (39,741,000)	$ (619,350,000)	$ 3,012,814,000	$ 54,525,000	$ 4,658,000	$ 3,071,997,000	$ 3,012,814,000	$ 54,525,000	$ 4,658,000
Noncontrolling Interest - Operating Partnership (Mezzanine) - Beginning Balance at Dec. 31, 2016	7,537,000								7,537,000
Increase (Decrease) in Temporary Equity [Roll Forward]
Net income (Mezzanine)	354,000								354,000
Distributions (Mezzanine)	(354,000)								(354,000)
Noncontrolling Interest - Operating Partnership (Mezzanine) - Ending Balance at Sep. 30, 2017	$ 7,537,000								$ 7,537,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
OPERATING ACTIVITIES
Net income	$ 158,221,000	$ 165,854,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	139,389,000	156,562,000
Amortization of deferred financing costs	2,811,000	3,068,000
Expensed pursuit costs	4,957,000	882,000
Impairment charges - real estate assets	9,650,000	0
Loss on debt extinguishment	0	(3,494,000)
Equity in earnings of unconsolidated joint ventures	(14,026,000)	(19,540,000)
Gain on property dispositions	(30,542,000)	(25,671,000)
Share-based compensation/Non-cash compensation	12,467,000	17,673,000
Other	(2,547,000)	(5,326,000)
Changes in operating assets and liabilities:
Restricted cash	(3,330,000)	4,059,000
Accounts receivable	1,976,000	(4,980,000)
Deferred rent receivable	(15,360,000)	(12,948,000)
Prepaid expenses and other assets	(28,115,000)	(23,054,000)
Accounts payable	13,249,000	21,343,000
Accrued interest	12,829,000	12,800,000
Other liabilities	(42,000)	(2,561,000)
Net cash provided by operating activities	261,587,000	291,655,000
INVESTING ACTIVITIES
Investment in properties - acquisitions	(62,327,000)	(9,278,000)
Investment in properties - other	(39,719,000)	(44,017,000)
Investments in and advances to unconsolidated joint ventures	(41,154,000)	(50,460,000)
Distributions from unconsolidated joint ventures	17,089,000	49,372,000
Net proceeds from disposition of properties/land	56,474,000	142,808,000
Investment in development in progress	(189,282,000)	(259,193,000)
Investment in land held for development	(93,813,000)	(70,809,000)
Payment of deferred leasing costs	(28,424,000)	(22,306,000)
Investing - Other	24,096,000	4,874,000
Net cash used in investing activities	(357,060,000)	(259,009,000)
FINANCING ACTIVITIES
Net proceeds from issuance of common shares	7,356,000	11,967,000
Share repurchase including shares related to tax withholdings	(4,879,000)	(45,728,000)
Proceeds from unsecured notes	0	396,648,000
Repayments of unsecured notes including prepayment premium	0	(303,673,000)
Repayments of mortgage loans	(5,974,000)	(25,260,000)
Proceeds from credit facility	486,000,000	466,300,000
Repayments on credit facility	(191,000,000)	(305,300,000)
Payment of deferred financing costs	(22,000)	(2,600,000)
Distribution paid on common shares	(187,625,000)	(209,428,000)
Distribution paid on units	(5,450,000)	(5,690,000)
Net cash provided by (used in) financing activities	98,406,000	(22,764,000)
Net increase in cash and cash equivalents	2,933,000	9,882,000
Increase (decrease) in cash and cash equivalents related to foreign currency translation	1,091,000	(2,945,000)
Cash and cash equivalents at beginning of period	43,642,000	35,353,000
Cash and cash equivalents at end of period	47,666,000	42,290,000
Liberty Property Limited Partnership [Member]
OPERATING ACTIVITIES
Net income	158,221,000	165,854,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	139,389,000	156,562,000
Amortization of deferred financing costs	2,811,000	3,068,000
Expensed pursuit costs	4,957,000	882,000
Impairment charges - real estate assets	9,650,000	0
Loss on debt extinguishment	0	(3,494,000)
Equity in earnings of unconsolidated joint ventures	(14,026,000)	(19,540,000)
Gain on property dispositions	(30,542,000)	(25,671,000)
Share-based compensation/Non-cash compensation	12,467,000	17,673,000
Other	(2,547,000)	(5,326,000)
Changes in operating assets and liabilities:
Restricted cash	(3,330,000)	4,059,000
Accounts receivable	1,976,000	(4,980,000)
Deferred rent receivable	(15,360,000)	(12,948,000)
Prepaid expenses and other assets	(28,115,000)	(23,054,000)
Accounts payable	13,249,000	21,343,000
Accrued interest	12,829,000	12,800,000
Other liabilities	(42,000)	(2,561,000)
Net cash provided by operating activities	261,587,000	291,655,000
INVESTING ACTIVITIES
Investment in properties - acquisitions	(62,327,000)	(9,278,000)
Investment in properties - other	(39,719,000)	(44,017,000)
Investments in and advances to unconsolidated joint ventures	(41,154,000)	(50,460,000)
Distributions from unconsolidated joint ventures	17,089,000	49,372,000
Net proceeds from disposition of properties/land	56,474,000	142,808,000
Investment in development in progress	(189,282,000)	(259,193,000)
Investment in land held for development	(93,813,000)	(70,809,000)
Payment of deferred leasing costs	(28,424,000)	(22,306,000)
Investing - Other	24,096,000	4,874,000
Net cash used in investing activities	(357,060,000)	(259,009,000)
FINANCING ACTIVITIES
Proceeds from unsecured notes	0	396,648,000
Repayments of unsecured notes including prepayment premium	0	(303,673,000)
Repayments of mortgage loans	(5,974,000)	(25,260,000)
Proceeds from credit facility	486,000,000	466,300,000
Repayments on credit facility	(191,000,000)	(305,300,000)
Payment of deferred financing costs	(22,000)	(2,600,000)
Capital contributions	7,356,000	11,967,000
Distributions to partners/noncontrolling interests	(197,954,000)	(260,846,000)
Net cash provided by (used in) financing activities	98,406,000	(22,764,000)
Net increase in cash and cash equivalents	2,933,000	9,882,000
Increase (decrease) in cash and cash equivalents related to foreign currency translation	1,091,000	(2,945,000)
Cash and cash equivalents at beginning of period	43,642,000	35,353,000
Cash and cash equivalents at end of period	$ 47,666,000	$ 42,290,000

Organization and Basis of Prese

Organization and Basis of Presentation	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]	Organization and Basis of Presentation Organization Liberty Property Trust (the “Trust”) is a self-administered and self-managed Maryland real estate investment trust (a “REIT”). Substantially all of the Trust’s assets are owned directly or indirectly, and substantially all of the Trust’s operations are conducted directly or indirectly, by its subsidiary, Liberty Property Limited Partnership, a Pennsylvania limited partnership (the “Operating Partnership” and, together with the Trust and their consolidated subsidiaries, the “Company”). The Trust is the sole general partner and also a limited partner of the Operating Partnership, owning 97.7% of the common equity of the Operating Partnership at September 30, 2017 . The Company owns and operates industrial properties nationally and owns and operates office properties in a focused group of office markets. Additionally, the Company owns certain assets in the United Kingdom. Unless otherwise indicated, the notes to the Consolidated Financial Statements apply to both the Trust and the Operating Partnership. The terms the “Company,” “we,” “our” and “us” mean the Trust and Operating Partnership collectively. The Operating Partnership is a variable interest entity ("VIE") of the Trust as the limited partners do not have substantive kick-out or participating rights. The Trust is the primary beneficiary of the Operating Partnership as it has the power to direct the activities of the Operating Partnership and the rights to absorb 97.7% of the net income of the Operating Partnership. The Trust has no significant assets or liabilities other than its investment in the Operating Partnership. As the Operating Partnership is already consolidated in the balance sheets of the Trust, the identification of this entity as a VIE has no impact on the consolidated financial statements of the Trust. In addition, the Company holds a 20% interest in Liberty/Comcast 1701 JFK Boulevard, LP which was determined to be a VIE. The Company determined that it is not the primary beneficiary as the Company and its third party partner share control of the joint venture. The Company's maximum exposure to loss is equal to its equity investment in the joint venture which was $17.6 million and $18.7 million as of September 30, 2017 and December 31, 2016, respectively. Basis of Presentation The accompanying unaudited consolidated financial statements of the Company have been prepared in accordance with United States generally accepted accounting principles (“US GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by US GAAP for complete financial statements and should be read in conjunction with the consolidated financial statements and notes thereto included in the Annual Report on Form 10-K of the Company for the year ended December 31, 2016 . In the opinion of management, all adjustments (consisting solely of normal recurring adjustments) necessary for a fair presentation of the financial statements for these interim periods have been included. The results of interim periods are not necessarily indicative of the results to be obtained for a full fiscal year. In the fourth quarter of 2016, the Company entered into an agreement relating to the development, for a fee, of an office building at its Camden Waterfront project in Camden, NJ. Project revenues and related costs and expenses are presented on a gross basis as "Development service fee income" and "Development service fee expense" in the Consolidated Statements of Comprehensive Income. Additionally, at the same time, the Company began classifying development fees and expenses relating to its development fee arrangements for certain unconsolidated joint venture projects in a manner consistent with the Camden project described above. Previously, development service fee income relating to its unconsolidated joint ventures had been classified as other income and development service fee expense had been classified as general and administrative expense in amounts as follows: Three months ended Nine months ended September 30, 2016 September 30, 2016 Other income $ 1,219 $ 3,789 General and administrative $ 1,058 $ 3,210 In the first quarter of 2017, the Company adopted ASU 2016-09, Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”), which requires the Company to reclassify shares withheld for tax withholding purposes on share-based compensation awards from operating activities to financing activities. As a result of the adoption, a $4.8 million cash outflow has been reclassified in the September 30, 2016 consolidated statement of cash flows from operating activities to financing activities. In the third quarter of 2017, the Company began to separately classify expensed pursuit costs (see Note 7) in the Consolidated Statements of Comprehensive Income. These costs, which were reclassed retrospectively for all periods, were formerly classified as general and administrative expense. Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09"), which supersedes nearly all existing revenue recognition guidance (except revenue in the scope of other accounting standards, including standards related to leasing). Subsequently, the FASB issued the following standards related to ASU 2014-09: ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations; ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing ; ASU 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients ; and ASU 2017-13, Revenue from Contracts with Customers (Topic 606): Amendments to SEC Paragraphs Pursuant to the Staff Announcement at the July 20, 2017 EITF Meeting and Rescission of Prior SEC Staff Announcements and Observer Comments (collectively, the “New Revenue Standards”). The Company must adopt the New Revenue Standards effective January 1, 2018. The New Revenue Standards clarify the required factors that an entity must consider when recognizing revenue and require additional disclosures concerning contracts with customers, judgments concerning revenue recognition, and assets recognized for the costs to obtain or fulfill a contract. The Company continues to evaluate the New Revenue Standards by analyzing certain revenue streams. The Company concluded that there are no revenue streams from its lease agreements that are covered by the New Revenue Standards with the exception of non-lease components as further discussed. Once the new guidance setting forth principles for the recognition, measurement, presentation and disclosure of leases goes into effect on January 1, 2019, the Company believes that the New Revenue Standards will apply to components of revenue due under leases that are deemed to be non-lease components (such as common area maintenance and provision of utilities), which could affect the recognition pattern for such revenue. The Company continues to evaluate the qualitative and quantitative disclosure requirements of the New Revenue Standards. The Company does not expect the New Revenue Standards to have a material impact on the measurement and recognition of gains and losses on the sale of properties. The Company is in the process of evaluating any impact on the amount and timing of recognizing its development service fee income, which is currently accounted for under the percentage of completion method based on applicable costs incurred and estimated to be incurred. The Company continues to assess the impact from adopting the New Revenue Standards on its business processes, financial reporting disclosures, and internal controls over financial reporting (“ICFR”). Significant assessment and implementation matters to be addressed prior to adopting the New Revenue Standards include completing a review of certain customer contracts, determining the impact the new accounting standard will have on the Company’s financial statements and related disclosures, and updating, through the completion of the implementation, the Company’s business processes, systems, and controls required to comply with the New Revenue Standards. Upon completion of the Company’s implementation plan and evaluation of the remaining revenue contracts, the Company will adopt additional controls around ICFR and its business processes for any new and existing revenue arrangements. The Company is on target to complete its assessment of the New Revenue Standards and the impact on the Company’s financial statements and related disclosures as of January 1, 2018. Although the Company is still completing its analysis of the impact from adopting the New Revenue Standards, the Company does not anticipate the impact to be material and, as a result, the Company plans to adopt the New Revenue Standards using the modified retrospective method. In February 2016, the FASB issued ASU 2016-02, Leases ("ASU 2016-02"). ASU 2016-02 amends the existing accounting standards for lease accounting, including requiring lessees to recognize most leases on their balance sheets and making targeted changes to lessor accounting. ASU 2016-02 is effective for the Company beginning January 1, 2019. Early adoption of ASU 2016-02 is permitted. The standard requires a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application, with an option to use certain transition relief. For leases in which the Company is the lessor, the standard requires that the lease and non-lease components of the lease agreement should be separated. Revenue related to the lease component of the contract will be recognized on a straight-line basis, while revenue related to the non-lease component will be recognized under the provisions of the New Revenue Standards. For lease agreements longer than one year in which the Company is the lessee, the Company will measure the present value of the future lease payments and recognize a right-of-use asset and corresponding lease liability on its balance sheet. In addition, the new standard states that only direct leasing costs may be capitalized. The Company is evaluating the impact ASU 2016-02 will have on its financial position and results of operations. In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments (“ASU 2016-15”). ASU 2016-15 is designed to clarify how entities should classify cash receipts and cash payments in the statement of cash flows. ASU 2016-15 is effective for the Company beginning January 1, 2018. Early adoption of ASU 2016-15 is permitted. The standard requires retrospective application unless it is impracticable to do so. The Company is evaluating the impact ASU 2016-15 will have on its statement of cash flows. In February 2017, the FASB issued ASU 2017-05, Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets ("ASU 2017-05"). ASU 2017-05 is designed to provide guidance on how to recognize gain and losses on sales, including partial sale, of nonfinancial assets to noncustomers. ASU 2017-05 is effective for the Company beginning January 1, 2018. Early adoption is permitted but the standard is required to be adopted concurrently with the New Revenue Standards. The Company is evaluating the impact ASU 2017-05 will have on the Company's financial position and results of operations. In May 2017, the FASB issued ASU 2017-09, Scope of Modification Accounting ("ASU 2017-09"). ASU 2017-09 clarifies when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. ASU 2017-09 is effective for the Company beginning January 1, 2018. Early adoption is permitted. The new guidance will be applied prospectively to awards modified on or after the adoption date. The Company is evaluating the impact ASU 2017-09 will have on the Company's financial position and results of operations. In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities ("ASU 2017-12"). ASU 2017-12 is designed to better align a company’s financial reporting for hedging activities with the economic objectives of those activities. ASU 2017-12 is effective for the Company beginning January 1, 2019. Early adoption is permitted using a modified retrospective transition method. This adoption method will require the Company to recognize the cumulative effect of initially applying ASU 2017-12 as an adjustment to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year that an entity adopts the update. The Company is evaluating the impact ASU 2017-12 will have on the Company's financial position and results of operations.

Income per Common Share of the

Income per Common Share of the Trust	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Income per Common Share of the Trust The following table sets forth the computation of basic and diluted income per common share of the Trust (in thousands except per share amounts): For the Three Months Ended For the Three Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Shares (Denominator) Per Share Income (Numerator) Weighted Average Shares (Denominator) Per Share Net income available to common shareholders - basic $ 59,539 146,811 $ 0.41 $ 54,253 146,215 $ 0.37 Dilutive shares for long-term compensation plans — 785 — 892 Net income available to common shareholders - diluted $ 59,539 147,596 $ 0.40 $ 54,253 147,107 $ 0.37 For the Nine Months Ended For the Nine Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Shares (Denominator) Per Share Income (Numerator) Weighted Average Shares (Denominator) Per Share Net income available to common shareholders - basic $ 153,982 146,678 $ 1.05 $ 161,434 146,121 $ 1.10 Dilutive shares for long-term compensation plans — 752 — 667 Net income available to common shareholders - diluted $ 153,982 147,430 $ 1.04 $ 161,434 146,788 $ 1.10 Dilutive shares for long-term compensation plans represent the unvested common shares outstanding during the periods as well as the dilutive effect of outstanding options. There were no anti-dilutive options excluded from the computation of diluted income per common share for the three and nine months ended September 30, 2017 as compared to 160,000 and 762,000 , respectively, for the same periods in 2016 . During the three and nine months ended September 30, 2017 , 79,000 and 167,000 common shares, respectively, were issued upon the exercise of options. During the year ended December 31, 2016 , 369,000 common shares were issued upon the exercise of options. Share Repurchase The Company’s Board of Trustees has authorized a share repurchase plan under which the Company may purchase up to $250 million of the Company’s outstanding common shares through September 28, 2019. Purchases made pursuant to the program may be made in either the open market or in privately negotiated transactions from time to time as permitted by securities laws and other legal requirements. There were no purchases under the plan during the three or nine months ended September 30, 2017 .

Income per Common Unit of the O

Income per Common Unit of the Operating Partnership	9 Months Ended
	Sep. 30, 2017
Earnings Per Unit, Basic and Diluted [Line Items]
Earnings Per Share [Text Block]	Income per Common Share of the Trust The following table sets forth the computation of basic and diluted income per common share of the Trust (in thousands except per share amounts): For the Three Months Ended For the Three Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Shares (Denominator) Per Share Income (Numerator) Weighted Average Shares (Denominator) Per Share Net income available to common shareholders - basic $ 59,539 146,811 $ 0.41 $ 54,253 146,215 $ 0.37 Dilutive shares for long-term compensation plans — 785 — 892 Net income available to common shareholders - diluted $ 59,539 147,596 $ 0.40 $ 54,253 147,107 $ 0.37 For the Nine Months Ended For the Nine Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Shares (Denominator) Per Share Income (Numerator) Weighted Average Shares (Denominator) Per Share Net income available to common shareholders - basic $ 153,982 146,678 $ 1.05 $ 161,434 146,121 $ 1.10 Dilutive shares for long-term compensation plans — 752 — 667 Net income available to common shareholders - diluted $ 153,982 147,430 $ 1.04 $ 161,434 146,788 $ 1.10 Dilutive shares for long-term compensation plans represent the unvested common shares outstanding during the periods as well as the dilutive effect of outstanding options. There were no anti-dilutive options excluded from the computation of diluted income per common share for the three and nine months ended September 30, 2017 as compared to 160,000 and 762,000 , respectively, for the same periods in 2016 . During the three and nine months ended September 30, 2017 , 79,000 and 167,000 common shares, respectively, were issued upon the exercise of options. During the year ended December 31, 2016 , 369,000 common shares were issued upon the exercise of options. Share Repurchase The Company’s Board of Trustees has authorized a share repurchase plan under which the Company may purchase up to $250 million of the Company’s outstanding common shares through September 28, 2019. Purchases made pursuant to the program may be made in either the open market or in privately negotiated transactions from time to time as permitted by securities laws and other legal requirements. There were no purchases under the plan during the three or nine months ended September 30, 2017 .
Liberty Property Limited Partnership [Member]
Earnings Per Unit, Basic and Diluted [Line Items]
Earnings Per Share [Text Block]	Income per Common Unit of the Operating Partnership The following table sets forth the computation of basic and diluted income per common unit of the Operating Partnership (in thousands, except per unit amounts): For the Three Months Ended For the Three Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Units (Denominator) Per Unit Income (Numerator) Weighted Average Units (Denominator) Per Unit Net income - net of noncontrolling interest - consolidated joint ventures $ 61,084 $ 55,677 Less: Preferred unit distributions (118 ) (118 ) Net income available to common unitholders - basic $ 60,966 150,339 $ 0.41 $ 55,559 149,751 $ 0.37 Dilutive units for long-term compensation plans — 785 — 892 Net income available to common unitholders - diluted $ 60,966 151,124 $ 0.40 $ 55,559 150,643 $ 0.37 For the Nine Months Ended For the Nine Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Units (Denominator) Per Unit Income (Numerator) Weighted Average Units (Denominator) Per Unit Net income - net of noncontrolling interest - consolidated joint ventures $ 158,026 $ 165,684 Less: Preferred unit distributions (354 ) (354 ) Net income available to common unitholders - basic 157,672 150,206 $ 1.05 165,330 149,659 $ 1.10 Dilutive units for long-term compensation plans — 752 — 667 Net income available to common unitholders - diluted $ 157,672 150,958 $ 1.04 $ 165,330 150,326 $ 1.10 Dilutive units for long-term compensation plans represent the unvested common units outstanding during the periods as well as the dilutive effect of outstanding options. There were no anti-dilutive options excluded from the computation of diluted income per common unit for the three and nine months ended September 30, 2017 as compared to 160,000 and 762,000 , respectively, for the same periods in 2016 . During the three and nine months ended September 30, 2017 , 79,000 and 167,000 common units, respectively, were issued upon exercise of options. During the year ended December 31, 2016 , 369,000 common units were issued upon the exercise of options. Share Repurchase The Company’s Board of Trustees has authorized a share repurchase plan under which the Company may purchase up to $250 million of the Company’s outstanding common units through September 28, 2019. Purchases made pursuant to the program may be made in either the open market or in privately negotiated transactions from time to time as permitted by securities laws and other legal requirements. There were no purchases under the plan during the three or nine months ended September 30, 2017 .

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss) Note [Text Block]	Accumulated Other Comprehensive Loss The following table sets forth the components of Accumulated Other Comprehensive Loss (in thousands): As of and for the nine months ended September 30, 2017 2016 Foreign Currency Translation: Beginning balance $ (56,767 ) $ (22,023 ) Translation adjustment 16,314 (23,003 ) Ending balance (40,453 ) (45,026 ) Derivative Instruments: Beginning balance (455 ) (865 ) Unrealized gain (loss) (25 ) (1,955 ) Reclassification adjustment (1) 391 823 Ending balance (89 ) (1,997 ) Total accumulated other comprehensive loss (40,542 ) (47,023 ) Less: portion included in noncontrolling interest – operating partnership 801 951 Total accumulated other comprehensive loss included in shareholders' equity/owners' equity $ (39,741 ) $ (46,072 ) (1) Amounts reclassified out of Accumulated Other Comprehensive Loss/General & Limited Partner's Equity into contractual interest expense.

Real Estate

Real Estate	9 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Disposal Groups, Including Discontinued Operations, Disclosure [Text Block]	Real Estate Information on the operating properties and land parcels the Company acquired during the three and nine months ended September 30, 2017 is as follows: Three Months Ended September 30, 2017 Nine Months Ended September 30, 2017 Number of Buildings Acres of Developable Land Leaseable Square Feet Purchase Price (in thousands) Number of Buildings Acres of Developable Land Leaseable Square Feet Purchase Price (in thousands) Carolinas/Richmond — — — $ — — 11 — $ 1,242 Lehigh/Central PA — — — — — 95 — 17,798 United Kingdom — — — — — 35 — 12,550 Other: Arizona — — — — — 6 — 1,327 Atlanta — — — — — 80 — 2,867 DC Metro — — — — — 10 — 504 New Jersey 2 — 205,116 25,599 2 17 205,116 29,301 Southern California 1 — 149,275 16,650 2 — 249,855 35,760 3 — 354,391 $ 42,249 4 254 454,971 $ 101,349 Information on the operating properties and land parcels the Company sold or conveyed during the three and nine months ended September 30, 2017 is as follows: Three Months Ended September 30, 2017 Nine Months Ended September 30, 2017 Number of Buildings Acres of Developable Land Leaseable Square Feet Gross Proceeds (in thousands) Number of Buildings Acres of Developable Land Leaseable Square Feet Gross Proceeds (in thousands) Chicago/Minneapolis 2 — 104,994 $ 5,817 3 — 136,110 $ 8,917 Florida — 5 — 10,620 — 16 — 13,256 Houston — 19 — 2,275 — 26 — 4,270 Philadelphia — — — — — 2 — 6,904 Southeastern PA 1 — 28,495 2,765 3 3 123,908 11,815 Other — — — — — 6 — 3,739 3 24 133,489 $ 21,477 6 53 260,018 $ 48,901 During the three months ended September 30, 2017, a contingency related to a 2015 portfolio sale was settled and the Company recognized a deferred gain in the accompanying statements of comprehensive income in the amount of $14.3 million . Pursuant to a purchase option contained in its lease agreement, a tenant exercised its option to purchase, for an aggregate purchase price of $249.0 million , two industrial buildings totaling 1.7 million square feet and 44 acres of land held for development with a total carrying value of $176.4 million . These properties and land are located in the Company's Lehigh/Central PA reportable segment. As of September 30, 2017 these assets and liabilities were classified as held for sale on the Company's consolidated balance sheet. Additionally, the Company classified 9 acres of land held for development with a total carrying value of $1.1 million as assets held for sale due to an anticipated condemnation conveyance. The disposition is anticipated to occur in 2018. This land is located in the Company's Chicago-Minneapolis reportable segment.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Segment Information	Segment Information The Company owns and operates industrial properties nationally and owns and operates office properties in a focused group of office markets. Additionally, the Company owns certain assets in the United Kingdom. During the nine months ended September 30, 2017, the Company realigned its reportable segments as follows: • Carolinas/Richmond; • Chicago/Minneapolis; • Florida; • Houston; • Lehigh/Central PA; • Philadelphia; • Southeastern PA; and • United Kingdom. Certain other segments are aggregated into an "Other" category which includes the reportable segments: Arizona; Atlanta; Cincinnati/Columbus/Indianapolis; Dallas; DC Metro; New Jersey; and Southern California. Comparative prior periods have been restated to reflect current segment disclosures. The Company evaluates the performance of its reportable segments based on segment net operating income (“SNOI”). SNOI is defined as net operating income (rental revenue and operating expense reimbursements less rental property and real estate tax expenses) less amortization of lease transaction costs and other operating expenses which relate directly to the management and operation of the assets within each reportable segment. The Company's accounting policies for the segments are the same as those used in the Company's consolidated financial statements. There are no material inter-segment transactions. The operating information by reportable segment is as follows (in thousands): Three Months Nine Months Ended September 30, Ended September 30, 2017 2016 2017 2016 Operating revenue Carolinas/Richmond $ 18,910 $ 17,292 $ 55,192 $ 49,226 Chicago/Minneapolis 16,147 23,417 47,789 66,848 Florida 15,072 28,115 43,802 85,230 Houston 15,167 14,870 44,720 43,840 Lehigh/Central PA 40,698 34,157 122,048 102,182 Philadelphia 11,137 10,513 33,501 31,253 Southeastern PA 15,422 24,563 45,165 74,789 United Kingdom 3,773 3,275 10,204 10,352 Other 33,288 34,831 95,826 104,274 Segment-level operating revenue 169,614 191,033 498,247 567,994 Reconciliation to total operating revenues Development service fee income 24,176 — 53,920 — Other (137 ) (176 ) (18 ) (341 ) Total operating revenue $ 193,653 $ 190,857 $ 552,149 $ 567,653 SNOI Carolinas/Richmond $ 13,621 $ 12,198 $ 39,698 $ 34,257 Chicago/Minneapolis 9,554 12,519 28,913 35,761 Florida 10,176 18,340 29,686 53,129 Houston 8,701 7,989 23,263 24,858 Lehigh/Central PA 29,995 24,982 88,656 73,939 Philadelphia 8,743 7,750 25,987 23,089 Southeastern PA 9,246 16,244 25,866 44,544 United Kingdom 1,781 2,031 5,288 6,871 Other 21,901 23,201 64,089 68,980 SNOI 113,718 125,254 331,446 365,428 Reconciliation to net income Interest expense (23,060 ) (29,528 ) (67,345 ) (91,071 ) Loss on debt extinguishment — (3,494 ) — (3,494 ) Depreciation/amortization expense (1) (33,521 ) (34,896 ) (99,829 ) (113,855 ) Impairment charges - real estate assets (9,650 ) — (9,650 ) — Gain on property dispositions 23,840 1,318 30,542 25,671 Equity in earnings of unconsolidated joint ventures 4,305 9,043 14,026 19,540 General and administrative expense (1) (8,104 ) (10,406 ) (31,230 ) (33,910 ) Expensed pursuit costs (4,772 ) (772 ) (4,957 ) (882 ) Income taxes (1) (64 ) 17 (240 ) (1,203 ) Other (1,533 ) (802 ) (4,542 ) (370 ) Net income $ 61,159 $ 55,734 $ 158,221 $ 165,854 (1) Excludes costs which are included in determining SNOI. The Company's total assets by reportable segment as of September 30, 2017 and December 31, 2016 is as follows (in thousands): September 30, 2017 December 31, 2016 Carolinas/Richmond $ 518,279 $ 503,920 Chicago/Minnesota 611,656 616,298 Florida 518,169 514,431 Houston 514,622 530,438 Lehigh/Central PA 1,372,896 1,311,815 Philadelphia 651,108 557,510 Southeastern PA 256,378 262,155 United Kingdom 233,657 189,766 Other 1,563,244 1,403,431 Segment-level total assets 6,240,009 5,889,764 Corporate Other 69,665 103,049 Total assets $ 6,309,674 $ 5,992,813

Accounting for the Impairment o

Accounting for the Impairment of Long-Lived Assets and Fee Development Contracts	9 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Asset Impairment Charges [Text Block]	Accounting for the Impairment of Long-Lived Assets and Fee Development Contracts Impairment Charges - Real Estate Assets The Company disposes of and anticipates the potential disposition of certain properties prior to the end of their remaining useful lives. During the three and nine months ended September 30, 2017 the Company recognized $9.7 million in impairment charges which related to the Company's Houston reportable segment. There were no impairment charges recognized during the three or nine months ended September 30, 2016. The Company determined these impairments based on third party offer prices and quoted offer prices for comparable transactions which are Level 2 and Level 3 inputs, respectively, according to the fair value hierarchy established in ASC 820. These measurements have occurred as circumstances arise, and the resulting estimates of fair value are not necessarily reflective of measurements at the period’s end. The Company has applied reasonable additional estimates and judgments in evaluating each of its properties and land held for development and has determined that there were no additional valuation adjustments necessary at September 30, 2017 . Should external or internal circumstances change requiring the need to shorten the holding periods or adjust the estimated future cash flows of the Company’s assets, the Company could be required to record impairment charges in the future. Fee Development Contracts From time to time, the Company enters into contracts to develop properties on a fee basis for joint ventures in which the Company holds an interest or for unrelated third parties. In these cases the Company typically agrees to be responsible for all aspects of the development of the project (and, in certain instances, related infrastructure) and to guarantee the timely lien-free completion of construction of the project and the payment, subject to certain exceptions, of cost overruns incurred in the development of the project. If the Company encounters construction delays or unexpected costs in the development of these projects or is otherwise unable to recover the costs it incurs, the resulting unrecovered costs and potential payments to customers could generate losses that would adversely affect the Company's cash flow and net income. On a quarterly basis, the Company applies reasonable estimates and judgments to assess whether or not it is necessary to accrue any estimated future losses with respect to such contracts. There were no such losses recognized during the three or nine months ended September 30, 2017 or 2016. Should external or internal circumstances change requiring the Company to adjust the estimated future cash flows from these development contracts or that suggest that such development contracts may result in a loss, the Company could be required to record losses in the future. Expensed Pursuit Costs The Company capitalizes pre-development costs incurred in pursuit of new development opportunities for which the Company currently believes future development is probable. Future development is dependent upon various factors, including zoning and regulatory approval, rental market conditions and construction costs. Initial pre-development costs incurred for pursuits for which future development is not yet considered probable are expensed as incurred. In addition, if the status of a future development by the Company is no longer probable, any capitalized pre-development costs are written off with a charge to expense. The Company expensed costs related to pursuit costs of $4.8 million and $5.0 million for the three and nine months ended September 30, 2017 and $772,000 and $882,000 for the three and nine months ended September 30, 2016. These costs are included in expensed pursuit costs on the accompanying Consolidated Statements of Comprehensive Income.

Noncontrolling Interests of the

Noncontrolling Interests of the Trust	9 Months Ended
	Sep. 30, 2017
Stockholders' Equity Attributable to Noncontrolling Interest [Abstract]
Noncontrolling Interests	Noncontrolling Interests of the Trust Noncontrolling interests in the accompanying financial statements represent the interests of the common and preferred units in the Operating Partnership not held by the Trust. In addition, noncontrolling interests include third-party ownership interests in consolidated joint venture investments. Common units The common units of the Operating Partnership not held by the Trust outstanding as of September 30, 2017 have the same economic characteristics as common shares of the Trust. The 3.5 million outstanding common units of the Operating Partnership not held by the Trust share proportionately in the net income or loss and in any distributions of the Operating Partnership. The common units of the Operating Partnership not held by the Trust are redeemable at any time at the option of the holder. The Trust, as the sole general partner of the Operating Partnership, may at its option elect to settle the redemption in cash or through the exchange on a one-for-one basis with unregistered common shares of the Trust. The market value of the 3.5 million outstanding common units based on the closing price of the common shares of the Trust at September 30, 2017 was $ 144.9 million .

Limited Partners' Equity of the

Limited Partners' Equity of the Operating Partnership	9 Months Ended
	Sep. 30, 2017
Preferred Units [Line Items]
Noncontrolling Interest Disclosure [Text Block]	Noncontrolling Interests of the Trust Noncontrolling interests in the accompanying financial statements represent the interests of the common and preferred units in the Operating Partnership not held by the Trust. In addition, noncontrolling interests include third-party ownership interests in consolidated joint venture investments. Common units The common units of the Operating Partnership not held by the Trust outstanding as of September 30, 2017 have the same economic characteristics as common shares of the Trust. The 3.5 million outstanding common units of the Operating Partnership not held by the Trust share proportionately in the net income or loss and in any distributions of the Operating Partnership. The common units of the Operating Partnership not held by the Trust are redeemable at any time at the option of the holder. The Trust, as the sole general partner of the Operating Partnership, may at its option elect to settle the redemption in cash or through the exchange on a one-for-one basis with unregistered common shares of the Trust. The market value of the 3.5 million outstanding common units based on the closing price of the common shares of the Trust at September 30, 2017 was $ 144.9 million .
Liberty Property Limited Partnership [Member]
Preferred Units [Line Items]
Noncontrolling Interest Disclosure [Text Block]	Limited Partners' Equity and Noncontrolling Interest of the Operating Partnership Limited partners' equity in the accompanying financial statements represents the interests of the common and preferred units in the Operating Partnership not held by the Trust. The Operating Partnership's noncontrolling interest includes third-party ownership interests in consolidated joint venture investments. Common units The common units outstanding have the same economic characteristics as common shares of the Trust. The 3.5 million outstanding common units as of September 30, 2017 not held by the Trust are the limited partners' equity - common units held by persons and entities other than the Trust. The common units of the Operating Partnership not held by the Trust are redeemable at any time at the option of the holder. The Trust, as the sole general partner of the Operating Partnership, may at its option elect to settle the redemption in cash or through the exchange on a one-for-one basis with unregistered common shares of the Trust. The market value of the 3.5 million outstanding common units at September 30, 2017 based on the closing price of the common shares of the Trust at September 30, 2017 was $ 144.9 million .

Noncontrolling Interest - Opera

Noncontrolling Interest - Operating Partnership/Limited Partners' Equity - Preferred Units	9 Months Ended
	Sep. 30, 2017
Temporary Equity [Line Items]
Stockholders' Equity Note Disclosure [Text Block]	Noncontrolling Interest - Operating Partnership/Limited Partners' Equity - Preferred Units As of September 30, 2017 , the Company had outstanding the following cumulative preferred units of the Operating Partnership: ISSUE AMOUNT UNITS LIQUIDATION PREFERENCE DIVIDEND RATE (in 000’s) Series I-2 $ 7,537 301 $25 6.25 % The preferred units are putable at the holder's option at any time and are callable at the Operating Partnership's option after a stated period of time for cash.

Disclosure of Fair Value of Fin

Disclosure of Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2017
Debt Instrument, Fair Value Disclosure [Abstract]
Disclosure of Fair Value of Financial Instruments	Fair Value of Financial Instruments ASC 820, Fair Value Measurements and Disclosures, provides guidance on the fair value measurement of a financial asset or liability. Inputs used to develop fair value are classified in one of three categories: Level 1 inputs (quoted prices (unadjusted) in active markets for identical assets or liabilities), Level 2 inputs (inputs other than quoted prices that are observable for the asset or liability, either directly or indirectly) and Level 3 inputs (unobservable inputs for the asset or liability). The following disclosure of estimated fair value was determined by management using available market information and appropriate valuation methodologies. However, considerable judgment is necessary to interpret market data and develop estimated fair value. Accordingly, the following estimates are not necessarily indicative of the amounts the Company could have realized on disposition of the financial instruments at September 30, 2017 and December 31, 2016 . The use of different market assumptions and/or estimation methodologies may have a material effect on the estimated fair value amounts. The carrying value of cash and cash equivalents, restricted cash, accounts receivable, accounts payable, accrued interest, dividend and distributions payable and other liabilities are reasonable estimates of fair value because of the short-term nature of these instruments. The carrying value of the outstanding amounts under the Company's credit facility is a reasonable estimate of fair value because interest rates float at a rate based on LIBOR. The Company determines the fair value of its interest rate swaps by using the standard methodology of netting discounted future fixed cash payments with the discounted expected variable cash receipts. These variable cash receipts of interest rate swaps are based on expectations of future LIBOR interest rates (forward curves) estimated by observing market LIBOR interest rate curves. This is a Level 2 fair value calculation. Also, credit valuation adjustments are factored into the fair value calculations to account for potential nonperformance risk. These credit valuation adjustments were concluded to be not significant inputs for the fair value calculations for the periods presented. See Note 13 - Derivative Instruments. The Company used a discounted cash flow model to determine the estimated fair value of its debt as of September 30, 2017 and December 31, 2016 . This is a Level 3 fair value calculation. The inputs used in preparing the discounted cash flow model include actual maturity dates and scheduled cash flows as well as estimates for market value discount rates. The Company updates the discounted cash flow model on a quarterly basis to reflect any changes in the Company's debt holdings and changes to discount rate assumptions. The following summarizes the fair value of the Company's mortgage loans and unsecured notes as of December 31, 2016 and September 30, 2017 (in thousands): Mortgage Loans Unsecured Notes Carrying Value Fair Value Carrying Value Fair Value As of December 31, 2016 $ 276,650 $ 286,684 $ 2,280,286 $ 2,340,762 As of September 30, 2017 $ 269,380 $ 281,671 $ 2,282,828 $ 2,379,014

Unconsolidated Joint Ventures

Unconsolidated Joint Ventures	9 Months Ended
	Sep. 30, 2017
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments and Joint Ventures Disclosure [Text Block]	Unconsolidated Joint Ventures Cambridge Medipark Ltd During the three and nine months ended September 30, 2017 and 2016, Cambridge Medipark, Ltd (a joint venture in which the Company holds a 50% interest) recognized gains on the sale of land leasehold interests. The Company's share of these gains was $1.3 million and $5.8 million , respectively, for the three and nine months ended September 30, 2017 compared to $3.3 million and $3.5 million , respectively, for the same periods in 2016. Liberty Property 19th & Arch LP During the three months ended September 30, 2017, Liberty Property 19th & Arch LP (a joint venture in which the Company holds a 20% interest) acquired one redevelopment property containing 48,031 square feet of leaseable space for a purchase price of $15.0 million .

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Interest rate swaps [Text Block]	Derivative Instruments The Company borrows funds at a combination of fixed and variable rates. Borrowings under the Company's revolving credit facility and certain bank mortgage loans bear interest at variable rates. Our long-term debt typically bears interest at fixed rates. The Company's interest rate risk management objectives are to limit generally the impact of interest rate changes on earnings and cash flows and to lower the Company's overall borrowing costs. To achieve these objectives, from time to time, the Company enters into interest rate hedge contracts such as collars, swaps, caps and treasury lock agreements in order to mitigate our interest rate risk with respect to various debt instruments. The Company generally does not hold or issue these derivative contracts for trading or speculative purposes. Interest rate swaps involve the receipt of variable-rate amounts from a counterparty in exchange for making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount. The effective portion of changes in the fair value of derivatives designated and that qualify as cash flow hedges is recorded in accumulated other comprehensive loss (for the Trust) and general partner's equity and limited partners ’ equity - common units (for the Operating Partnership) and is subsequently reclassified into interest expense in the period that the hedged forecasted transaction affects earnings. The Company determines the fair value of its interest rate swaps by using the standard methodology of netting discounted future fixed cash payments with the discounted expected variable cash receipts. These variable cash receipts of interest rate swaps are based on expectations of future LIBOR interest rates (forward curves) estimated by observing market LIBOR interest rate curves. This is a Level 2 fair value calculation. Also, credit valuation adjustments are factored into the fair value calculations to account for potential nonperformance risk. These credit valuation adjustments were concluded to be not significant inputs for the fair value calculations for the periods presented. The Company holds an interest in three interest rate swap contracts (“Swaps”) that eliminate the impact of changes in interest rates on the payments required under variable rate mortgages. The Swaps had aggregate notional amounts of $96.9 million and $98.9 million at September 30, 2017 and December 31, 2016 , respectively, and expire at various dates between 2018 and 2020 . The Company accounts for the effective portion of changes in the fair value of a derivative in accumulated other comprehensive loss and subsequently reclassifies the effective portion to earnings over the term that the hedged transaction affects earnings. The Company accounts for the ineffective portion of changes in the fair value of a derivative directly in earnings. The following table presents the location in the financial statements of the gains or losses recognized related to the Company’s cash flow hedges for the three and nine months ended September 30, 2017 and 2016 (in thousands): Three Months Ended Nine Months Ended September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Amount of gain (loss) related to the effective portion recognized in other comprehensive income (loss) $ 19 $ 415 $ (7 ) $ (1,928 ) Amount of loss related to the effective portion subsequently reclassified to interest expense $ (75 ) $ (264 ) $ (391 ) $ (823 ) Amount of (loss) gain related to the ineffective portion recognized in interest expense $ (8 ) $ 7 $ 5 $ (71 ) The fair value of the Swaps in the amounts of $3.1 million and $4.9 million as of September 30, 2017 and December 31, 2016 , respectively, is included in other liabilities in the accompanying consolidated balance sheets. The Company estimates that $0.2 million will be reclassified from accumulated other comprehensive loss as an increase to interest expense over the next 12 months. The Company has agreements with its derivative counterparties that contain a provision whereby if the Company defaults on any of its indebtedness, including defaults where repayment of the indebtedness has not been accelerated by the lender, then the Company could also be declared in default on its derivative obligations. If the Company were to breach any of the contractual provisions of the derivative contracts, it would be required to settle its obligations under the agreements at their termination value including accrued interest, which totaled approximately $3.1 million as of September 30, 2017 .

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Environmental Matters Substantially all of the Company's properties and land were subject to Phase I Environmental Assessments and when appropriate Phase II Environmental Assessments (collectively, the “Environmental Assessments”) obtained in contemplation of their acquisition by the Company or obtained by predecessor owners prior to the sale of the property or land to the Company. The Environmental Assessments did not reveal, nor is the Company aware of, any non-compliance with environmental laws, environmental liability or other environmental claim that the Company believes would likely have a material adverse effect on the Company. Operating Ground Lease Agreements Future minimum rental payments under the terms of all non-cancelable operating ground leases under which the Company is the lessee, as of September 30, 2017 , were as follows (in thousands): Year Amount 2017 (remaining) $ 443 2018 1,767 2019 1,767 2020 1,767 2021 1,767 2022 and thereafter 34,905 Total $ 42,416 Operating ground lease expense for the three and nine months ended September 30, 2017 was $313,000 and $936,000 , respectively, as compared to $241,000 and $734,000 , respectively, for the same periods in 2016 . Legal Matters From time to time, the Company is a party to a variety of legal proceedings, claims and assessments arising in the normal course of business. As of September 30, 2017 there were no legal proceedings, claims or assessments that the Company expects to have a material adverse effect on the Company’s business or financial statements. Other As of September 30, 2017 , the Company had letter of credit obligations of $6.3 million . As of September 30, 2017 , the Company had 24 buildings under development. These buildings are expected to contain, when completed, a total of 5.9 million square feet of leasable space and represent an anticipated aggregate investment of $560.8 million . At September 30, 2017 , development in progress totaled $395.1 million . In addition, as of September 30, 2017 , the Company had invested $14.4 million in deferred leasing costs related to these development buildings. As of September 30, 2017 , the Company was committed to $8.3 million in improvements on certain buildings and land parcels. As of September 30, 2017 , the Company was committed to $35.6 million in future land acquisitions. The Company expects to complete these purchases during the year ended December 31, 2017. As of September 30, 2017 , the Company was obligated to pay for tenant improvements not yet completed for a maximum of $26.7 million . Unconsolidated joint ventures in which the Company holds an interest, and in another case an unrelated third party, have engaged the Company as the developer of certain development properties pursuant to development agreements. The Company agrees, in consideration for a development fee, to be responsible for all aspects of the development of the properties (and, in certain instances, related infrastructure) and to guarantee the timely lien-free completion of construction of the properties and the payment, subject to certain exceptions, of any cost overruns incurred in the development of the properties. The Company is currently developing four properties for its unconsolidated joint ventures which represent an anticipated aggregate investment by the joint ventures of $976.9 million . As of September 30, 2017 , the Company was also committed to approximately $170.1 million in costs related to its agreement to develop, on a fee basis, an office building and infrastructure improvements for American Water Works in Camden, New Jersey. As of September 30, 2017 , $71.8 million of these costs had been incurred. The Company maintains cash and cash equivalents at financial institutions. The combined account balances at each institution typically exceed FDIC insurance coverage and, as a result, there is a concentration of credit risk related to amounts on deposit in excess of FDIC insurance coverage. The Company believes the risk is not significant.

Supplemental Disclosure to Stat

Supplemental Disclosure to Statements of Cash Flows	9 Months Ended
	Sep. 30, 2017
Supplemental Cash Flow Information [Abstract]
Supplemental Disclosure to Statements of Cash Flows	Supplemental Disclosure to Consolidated Statements of Cash Flows The following are supplemental disclosures to the consolidated statements of cash flows for the nine months ended September 30, 2017 and 2016 (amounts in thousands): 2017 2016 Write-off of fully depreciated/amortized property and deferred costs $ 26,609 $ 26,349 Write-off of depreciated/amortized property and deferred costs due to sale $ 13,127 $ 34,513 Write-off of costs related to early debt extinguishment $ — $ 109 Redemption of noncontrolling interests - common units $ 27 $ 132 Unrealized gain (loss) on cash flow hedge $ 366 $ (1,132 ) Changes in accrued development capital expenditures $ 18,255 $ (7,522 ) Capitalized equity-based compensation $ 877 $ 980 Amounts paid in cash for deferred leasing costs incurred in connection with signed leases with tenants are paid in conjunction with improving (acquiring) property, plant and equipment. Such costs are not contained within net real estate. However, they are integral to the completion of a tenant lease and ultimately are related to the improvement and thus the value of the Company’s property, plant and equipment. They are therefore included in investing activities in the Company’s consolidated statements of cash flows.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2017
Subsequent Event [Line Items]
Subsequent Events [Text Block]	Subsequent Events Credit Facility In October 2017, the Company replaced its existing $800 million credit facility which was set to mature in March 2018 with a new $900 million unsecured credit facility. The new facility includes a revolving credit facility for aggregate borrowings up to $800 million (the "Revolving Credit Facility") and a delayed draw term loan facility aggregating up to $100 million . It matures in October 2021 and the Company has options to extend the maturity date for up to one additional year. Based upon the Company’s current credit ratings, borrowings under the Revolving Credit Facility bear interest at LIBOR plus 87.5 basis points and bear interest at LIBOR plus 95 basis points for delayed draw term loans. There is also a 15 basis point annual facility fee. The Revolving Credit Facility contains a competitive bid option, whereby participating lenders bid on the interest rate to be charged. This feature is available for up to 50% of the amount of the Revolving Credit Facility. The financial and other covenants under the new facility are similar to our previous credit facility. The Company expects to incur approximately $5.1 million of debt issuance costs associated with the new facility. Agreement of Sale On October 2, 2017 the Company entered into an agreement to sell 14 office properties totaling 641,000 square feet of leasable space for $75.4 million . The properties are in the Southeastern PA segment. The sale is currently anticipated to close in 2017, subject to the satisfaction of certain closing conditions.

Organization and Basis of Pre23

Organization and Basis of Presentation (Policy)	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
New Accounting Pronouncements, Policy [Policy Text Block]	Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09"), which supersedes nearly all existing revenue recognition guidance (except revenue in the scope of other accounting standards, including standards related to leasing). Subsequently, the FASB issued the following standards related to ASU 2014-09: ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations; ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing ; ASU 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients ; and ASU 2017-13, Revenue from Contracts with Customers (Topic 606): Amendments to SEC Paragraphs Pursuant to the Staff Announcement at the July 20, 2017 EITF Meeting and Rescission of Prior SEC Staff Announcements and Observer Comments (collectively, the “New Revenue Standards”). The Company must adopt the New Revenue Standards effective January 1, 2018. The New Revenue Standards clarify the required factors that an entity must consider when recognizing revenue and require additional disclosures concerning contracts with customers, judgments concerning revenue recognition, and assets recognized for the costs to obtain or fulfill a contract. The Company continues to evaluate the New Revenue Standards by analyzing certain revenue streams. The Company concluded that there are no revenue streams from its lease agreements that are covered by the New Revenue Standards with the exception of non-lease components as further discussed. Once the new guidance setting forth principles for the recognition, measurement, presentation and disclosure of leases goes into effect on January 1, 2019, the Company believes that the New Revenue Standards will apply to components of revenue due under leases that are deemed to be non-lease components (such as common area maintenance and provision of utilities), which could affect the recognition pattern for such revenue. The Company continues to evaluate the qualitative and quantitative disclosure requirements of the New Revenue Standards. The Company does not expect the New Revenue Standards to have a material impact on the measurement and recognition of gains and losses on the sale of properties. The Company is in the process of evaluating any impact on the amount and timing of recognizing its development service fee income, which is currently accounted for under the percentage of completion method based on applicable costs incurred and estimated to be incurred. The Company continues to assess the impact from adopting the New Revenue Standards on its business processes, financial reporting disclosures, and internal controls over financial reporting (“ICFR”). Significant assessment and implementation matters to be addressed prior to adopting the New Revenue Standards include completing a review of certain customer contracts, determining the impact the new accounting standard will have on the Company’s financial statements and related disclosures, and updating, through the completion of the implementation, the Company’s business processes, systems, and controls required to comply with the New Revenue Standards. Upon completion of the Company’s implementation plan and evaluation of the remaining revenue contracts, the Company will adopt additional controls around ICFR and its business processes for any new and existing revenue arrangements. The Company is on target to complete its assessment of the New Revenue Standards and the impact on the Company’s financial statements and related disclosures as of January 1, 2018. Although the Company is still completing its analysis of the impact from adopting the New Revenue Standards, the Company does not anticipate the impact to be material and, as a result, the Company plans to adopt the New Revenue Standards using the modified retrospective method. In February 2016, the FASB issued ASU 2016-02, Leases ("ASU 2016-02"). ASU 2016-02 amends the existing accounting standards for lease accounting, including requiring lessees to recognize most leases on their balance sheets and making targeted changes to lessor accounting. ASU 2016-02 is effective for the Company beginning January 1, 2019. Early adoption of ASU 2016-02 is permitted. The standard requires a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application, with an option to use certain transition relief. For leases in which the Company is the lessor, the standard requires that the lease and non-lease components of the lease agreement should be separated. Revenue related to the lease component of the contract will be recognized on a straight-line basis, while revenue related to the non-lease component will be recognized under the provisions of the New Revenue Standards. For lease agreements longer than one year in which the Company is the lessee, the Company will measure the present value of the future lease payments and recognize a right-of-use asset and corresponding lease liability on its balance sheet. In addition, the new standard states that only direct leasing costs may be capitalized. The Company is evaluating the impact ASU 2016-02 will have on its financial position and results of operations. In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments (“ASU 2016-15”). ASU 2016-15 is designed to clarify how entities should classify cash receipts and cash payments in the statement of cash flows. ASU 2016-15 is effective for the Company beginning January 1, 2018. Early adoption of ASU 2016-15 is permitted. The standard requires retrospective application unless it is impracticable to do so. The Company is evaluating the impact ASU 2016-15 will have on its statement of cash flows. In February 2017, the FASB issued ASU 2017-05, Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets ("ASU 2017-05"). ASU 2017-05 is designed to provide guidance on how to recognize gain and losses on sales, including partial sale, of nonfinancial assets to noncustomers. ASU 2017-05 is effective for the Company beginning January 1, 2018. Early adoption is permitted but the standard is required to be adopted concurrently with the New Revenue Standards. The Company is evaluating the impact ASU 2017-05 will have on the Company's financial position and results of operations. In May 2017, the FASB issued ASU 2017-09, Scope of Modification Accounting ("ASU 2017-09"). ASU 2017-09 clarifies when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. ASU 2017-09 is effective for the Company beginning January 1, 2018. Early adoption is permitted. The new guidance will be applied prospectively to awards modified on or after the adoption date. The Company is evaluating the impact ASU 2017-09 will have on the Company's financial position and results of operations. In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities ("ASU 2017-12"). ASU 2017-12 is designed to better align a company’s financial reporting for hedging activities with the economic objectives of those activities. ASU 2017-12 is effective for the Company beginning January 1, 2019. Early adoption is permitted using a modified retrospective transition method. This adoption method will require the Company to recognize the cumulative effect of initially applying ASU 2017-12 as an adjustment to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year that an entity adopts the update. The Company is evaluating the impact ASU 2017-12 will have on the Company's financial position and results of operations.

Segment Information (Policies)

Segment Information (Policies)	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Segment Reporting, Policy [Policy Text Block]	The Company evaluates the performance of its reportable segments based on segment net operating income (“SNOI”). SNOI is defined as net operating income (rental revenue and operating expense reimbursements less rental property and real estate tax expenses) less amortization of lease transaction costs and other operating expenses which relate directly to the management and operation of the assets within each reportable segment.

Disclosure of Fair Value of F25

Disclosure of Fair Value of Financial Instruments Fair Value of Financial Instruments (Policies)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments, Policy [Policy Text Block]	ASC 820, Fair Value Measurements and Disclosures, provides guidance on the fair value measurement of a financial asset or liability. Inputs used to develop fair value are classified in one of three categories: Level 1 inputs (quoted prices (unadjusted) in active markets for identical assets or liabilities), Level 2 inputs (inputs other than quoted prices that are observable for the asset or liability, either directly or indirectly) and Level 3 inputs (unobservable inputs for the asset or liability). The following disclosure of estimated fair value was determined by management using available market information and appropriate valuation methodologies. However, considerable judgment is necessary to interpret market data and develop estimated fair value. Accordingly, the following estimates are not necessarily indicative of the amounts the Company could have realized on disposition of the financial instruments at September 30, 2017 and December 31, 2016 . The use of different market assumptions and/or estimation methodologies may have a material effect on the estimated fair value amounts. The carrying value of cash and cash equivalents, restricted cash, accounts receivable, accounts payable, accrued interest, dividend and distributions payable and other liabilities are reasonable estimates of fair value because of the short-term nature of these instruments. The carrying value of the outstanding amounts under the Company's credit facility is a reasonable estimate of fair value because interest rates float at a rate based on LIBOR. The Company determines the fair value of its interest rate swaps by using the standard methodology of netting discounted future fixed cash payments with the discounted expected variable cash receipts. These variable cash receipts of interest rate swaps are based on expectations of future LIBOR interest rates (forward curves) estimated by observing market LIBOR interest rate curves. This is a Level 2 fair value calculation. Also, credit valuation adjustments are factored into the fair value calculations to account for potential nonperformance risk. These credit valuation adjustments were concluded to be not significant inputs for the fair value calculations for the periods presented. See Note 13 - Derivative Instruments. The Company used a discounted cash flow model to determine the estimated fair value of its debt as of September 30, 2017 and December 31, 2016 . This is a Level 3 fair value calculation. The inputs used in preparing the discounted cash flow model include actual maturity dates and scheduled cash flows as well as estimates for market value discount rates. The Company updates the discounted cash flow model on a quarterly basis to reflect any changes in the Company's debt holdings and changes to discount rate assumptions.

Organization and Basis of Pre26

Organization and Basis of Presentation Basis of Presentation (Tables)	9 Months Ended
	Sep. 30, 2017
Basis of Presentation [Abstract]
Schedule of Adjustments to Previously Reported Financial Statements	Previously, development service fee income relating to its unconsolidated joint ventures had been classified as other income and development service fee expense had been classified as general and administrative expense in amounts as follows: Three months ended Nine months ended September 30, 2016 September 30, 2016 Other income $ 1,219 $ 3,789 General and administrative $ 1,058 $ 3,210

Income per Common Share of th27

Income per Common Share of the Trust (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table sets forth the computation of basic and diluted income per common share of the Trust (in thousands except per share amounts): For the Three Months Ended For the Three Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Shares (Denominator) Per Share Income (Numerator) Weighted Average Shares (Denominator) Per Share Net income available to common shareholders - basic $ 59,539 146,811 $ 0.41 $ 54,253 146,215 $ 0.37 Dilutive shares for long-term compensation plans — 785 — 892 Net income available to common shareholders - diluted $ 59,539 147,596 $ 0.40 $ 54,253 147,107 $ 0.37 For the Nine Months Ended For the Nine Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Shares (Denominator) Per Share Income (Numerator) Weighted Average Shares (Denominator) Per Share Net income available to common shareholders - basic $ 153,982 146,678 $ 1.05 $ 161,434 146,121 $ 1.10 Dilutive shares for long-term compensation plans — 752 — 667 Net income available to common shareholders - diluted $ 153,982 147,430 $ 1.04 $ 161,434 146,788 $ 1.10

Income per Common Unit of the28

Income per Common Unit of the Operating Partnership (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Unit, Basic and Diluted [Line Items]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table sets forth the computation of basic and diluted income per common share of the Trust (in thousands except per share amounts): For the Three Months Ended For the Three Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Shares (Denominator) Per Share Income (Numerator) Weighted Average Shares (Denominator) Per Share Net income available to common shareholders - basic $ 59,539 146,811 $ 0.41 $ 54,253 146,215 $ 0.37 Dilutive shares for long-term compensation plans — 785 — 892 Net income available to common shareholders - diluted $ 59,539 147,596 $ 0.40 $ 54,253 147,107 $ 0.37 For the Nine Months Ended For the Nine Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Shares (Denominator) Per Share Income (Numerator) Weighted Average Shares (Denominator) Per Share Net income available to common shareholders - basic $ 153,982 146,678 $ 1.05 $ 161,434 146,121 $ 1.10 Dilutive shares for long-term compensation plans — 752 — 667 Net income available to common shareholders - diluted $ 153,982 147,430 $ 1.04 $ 161,434 146,788 $ 1.10
Liberty Property Limited Partnership [Member]
Earnings Per Unit, Basic and Diluted [Line Items]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table sets forth the computation of basic and diluted income per common unit of the Operating Partnership (in thousands, except per unit amounts): For the Three Months Ended For the Three Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Units (Denominator) Per Unit Income (Numerator) Weighted Average Units (Denominator) Per Unit Net income - net of noncontrolling interest - consolidated joint ventures $ 61,084 $ 55,677 Less: Preferred unit distributions (118 ) (118 ) Net income available to common unitholders - basic $ 60,966 150,339 $ 0.41 $ 55,559 149,751 $ 0.37 Dilutive units for long-term compensation plans — 785 — 892 Net income available to common unitholders - diluted $ 60,966 151,124 $ 0.40 $ 55,559 150,643 $ 0.37 For the Nine Months Ended For the Nine Months Ended September 30, 2017 September 30, 2016 Income (Numerator) Weighted Average Units (Denominator) Per Unit Income (Numerator) Weighted Average Units (Denominator) Per Unit Net income - net of noncontrolling interest - consolidated joint ventures $ 158,026 $ 165,684 Less: Preferred unit distributions (354 ) (354 ) Net income available to common unitholders - basic 157,672 150,206 $ 1.05 165,330 149,659 $ 1.10 Dilutive units for long-term compensation plans — 752 — 667 Net income available to common unitholders - diluted $ 157,672 150,958 $ 1.04 $ 165,330 150,326 $ 1.10

Accumulated Other Comprehensi29

Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following table sets forth the components of Accumulated Other Comprehensive Loss (in thousands): As of and for the nine months ended September 30, 2017 2016 Foreign Currency Translation: Beginning balance $ (56,767 ) $ (22,023 ) Translation adjustment 16,314 (23,003 ) Ending balance (40,453 ) (45,026 ) Derivative Instruments: Beginning balance (455 ) (865 ) Unrealized gain (loss) (25 ) (1,955 ) Reclassification adjustment (1) 391 823 Ending balance (89 ) (1,997 ) Total accumulated other comprehensive loss (40,542 ) (47,023 ) Less: portion included in noncontrolling interest – operating partnership 801 951 Total accumulated other comprehensive loss included in shareholders' equity/owners' equity $ (39,741 ) $ (46,072 ) (1) Amounts reclassified out of Accumulated Other Comprehensive Loss/General & Limited Partner's Equity into contractual interest expense.

Real Estate (Tables)

Real Estate (Tables)	9 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment [Table Text Block]	Information on the operating properties and land parcels the Company acquired during the three and nine months ended September 30, 2017 is as follows: Three Months Ended September 30, 2017 Nine Months Ended September 30, 2017 Number of Buildings Acres of Developable Land Leaseable Square Feet Purchase Price (in thousands) Number of Buildings Acres of Developable Land Leaseable Square Feet Purchase Price (in thousands) Carolinas/Richmond — — — $ — — 11 — $ 1,242 Lehigh/Central PA — — — — — 95 — 17,798 United Kingdom — — — — — 35 — 12,550 Other: Arizona — — — — — 6 — 1,327 Atlanta — — — — — 80 — 2,867 DC Metro — — — — — 10 — 504 New Jersey 2 — 205,116 25,599 2 17 205,116 29,301 Southern California 1 — 149,275 16,650 2 — 249,855 35,760 3 — 354,391 $ 42,249 4 254 454,971 $ 101,349 Information on the operating properties and land parcels the Company sold or conveyed during the three and nine months ended September 30, 2017 is as follows: Three Months Ended September 30, 2017 Nine Months Ended September 30, 2017 Number of Buildings Acres of Developable Land Leaseable Square Feet Gross Proceeds (in thousands) Number of Buildings Acres of Developable Land Leaseable Square Feet Gross Proceeds (in thousands) Chicago/Minneapolis 2 — 104,994 $ 5,817 3 — 136,110 $ 8,917 Florida — 5 — 10,620 — 16 — 13,256 Houston — 19 — 2,275 — 26 — 4,270 Philadelphia — — — — — 2 — 6,904 Southeastern PA 1 — 28,495 2,765 3 3 123,908 11,815 Other — — — — — 6 — 3,739 3 24 133,489 $ 21,477 6 53 260,018 $ 48,901

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment, Revenue and Net Operating Income [Table Text Block]	The operating information by reportable segment is as follows (in thousands): Three Months Nine Months Ended September 30, Ended September 30, 2017 2016 2017 2016 Operating revenue Carolinas/Richmond $ 18,910 $ 17,292 $ 55,192 $ 49,226 Chicago/Minneapolis 16,147 23,417 47,789 66,848 Florida 15,072 28,115 43,802 85,230 Houston 15,167 14,870 44,720 43,840 Lehigh/Central PA 40,698 34,157 122,048 102,182 Philadelphia 11,137 10,513 33,501 31,253 Southeastern PA 15,422 24,563 45,165 74,789 United Kingdom 3,773 3,275 10,204 10,352 Other 33,288 34,831 95,826 104,274 Segment-level operating revenue 169,614 191,033 498,247 567,994 Reconciliation to total operating revenues Development service fee income 24,176 — 53,920 — Other (137 ) (176 ) (18 ) (341 ) Total operating revenue $ 193,653 $ 190,857 $ 552,149 $ 567,653 SNOI Carolinas/Richmond $ 13,621 $ 12,198 $ 39,698 $ 34,257 Chicago/Minneapolis 9,554 12,519 28,913 35,761 Florida 10,176 18,340 29,686 53,129 Houston 8,701 7,989 23,263 24,858 Lehigh/Central PA 29,995 24,982 88,656 73,939 Philadelphia 8,743 7,750 25,987 23,089 Southeastern PA 9,246 16,244 25,866 44,544 United Kingdom 1,781 2,031 5,288 6,871 Other 21,901 23,201 64,089 68,980 SNOI 113,718 125,254 331,446 365,428 Reconciliation to net income Interest expense (23,060 ) (29,528 ) (67,345 ) (91,071 ) Loss on debt extinguishment — (3,494 ) — (3,494 ) Depreciation/amortization expense (1) (33,521 ) (34,896 ) (99,829 ) (113,855 ) Impairment charges - real estate assets (9,650 ) — (9,650 ) — Gain on property dispositions 23,840 1,318 30,542 25,671 Equity in earnings of unconsolidated joint ventures 4,305 9,043 14,026 19,540 General and administrative expense (1) (8,104 ) (10,406 ) (31,230 ) (33,910 ) Expensed pursuit costs (4,772 ) (772 ) (4,957 ) (882 ) Income taxes (1) (64 ) 17 (240 ) (1,203 ) Other (1,533 ) (802 ) (4,542 ) (370 ) Net income $ 61,159 $ 55,734 $ 158,221 $ 165,854 (1) Excludes costs which are included in determining SNOI.
Assets by Segment and Reconciliation to Consolidated [Table Text Block]	The Company's total assets by reportable segment as of September 30, 2017 and December 31, 2016 is as follows (in thousands): September 30, 2017 December 31, 2016 Carolinas/Richmond $ 518,279 $ 503,920 Chicago/Minnesota 611,656 616,298 Florida 518,169 514,431 Houston 514,622 530,438 Lehigh/Central PA 1,372,896 1,311,815 Philadelphia 651,108 557,510 Southeastern PA 256,378 262,155 United Kingdom 233,657 189,766 Other 1,563,244 1,403,431 Segment-level total assets 6,240,009 5,889,764 Corporate Other 69,665 103,049 Total assets $ 6,309,674 $ 5,992,813

Noncontrolling Interest - Ope32

Noncontrolling Interest - Operating Partnership/Limited Partners' Equity - Preferred Units (Tables)	9 Months Ended
	Sep. 30, 2017
Temporary Equity [Line Items]
Schedule of Temporary Equity [Table Text Block]	As of September 30, 2017 , the Company had outstanding the following cumulative preferred units of the Operating Partnership: ISSUE AMOUNT UNITS LIQUIDATION PREFERENCE DIVIDEND RATE (in 000’s) Series I-2 $ 7,537 301 $25 6.25 %

Disclosure of Fair Value of F33

Disclosure of Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2017
Debt Instrument, Fair Value Disclosure [Abstract]
Fair Value, by Balance Sheet Grouping [Table Text Block]	The following summarizes the fair value of the Company's mortgage loans and unsecured notes as of December 31, 2016 and September 30, 2017 (in thousands): Mortgage Loans Unsecured Notes Carrying Value Fair Value Carrying Value Fair Value As of December 31, 2016 $ 276,650 $ 286,684 $ 2,280,286 $ 2,340,762 As of September 30, 2017 $ 269,380 $ 281,671 $ 2,282,828 $ 2,379,014

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments, Gain (Loss) [Table Text Block]	The following table presents the location in the financial statements of the gains or losses recognized related to the Company’s cash flow hedges for the three and nine months ended September 30, 2017 and 2016 (in thousands): Three Months Ended Nine Months Ended September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Amount of gain (loss) related to the effective portion recognized in other comprehensive income (loss) $ 19 $ 415 $ (7 ) $ (1,928 ) Amount of loss related to the effective portion subsequently reclassified to interest expense $ (75 ) $ (264 ) $ (391 ) $ (823 ) Amount of (loss) gain related to the ineffective portion recognized in interest expense $ (8 ) $ 7 $ 5 $ (71 )

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Rental Payments	Future minimum rental payments under the terms of all non-cancelable operating ground leases under which the Company is the lessee, as of September 30, 2017 , were as follows (in thousands): Year Amount 2017 (remaining) $ 443 2018 1,767 2019 1,767 2020 1,767 2021 1,767 2022 and thereafter 34,905 Total $ 42,416

Supplemental Disclosure to St36

Supplemental Disclosure to Statements of Cash Flows (Tables)	9 Months Ended
	Sep. 30, 2017
Supplemental Cash Flow Information [Abstract]
Supplemental Disclosure to Statements of Cash Flows	The following are supplemental disclosures to the consolidated statements of cash flows for the nine months ended September 30, 2017 and 2016 (amounts in thousands): 2017 2016 Write-off of fully depreciated/amortized property and deferred costs $ 26,609 $ 26,349 Write-off of depreciated/amortized property and deferred costs due to sale $ 13,127 $ 34,513 Write-off of costs related to early debt extinguishment $ — $ 109 Redemption of noncontrolling interests - common units $ 27 $ 132 Unrealized gain (loss) on cash flow hedge $ 366 $ (1,132 ) Changes in accrued development capital expenditures $ 18,255 $ (7,522 ) Capitalized equity-based compensation $ 877 $ 980

Organization and Basis of Pre37

Organization and Basis of Presentation (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Ownership interest in operating partnership - Limited Partnership	97.70%
Liberty Comcast 1701 JFK Boulevard, LP [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Ownership Percentage	20.00%
Liberty Comcast 1701 JFK Boulevard, LP [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Other Investments [Member]
Variable Interest Entity [Line Items]
Equity investment in joint venture	$ 17.6	$ 18.7
Maximum exposure to loss	$ 17.6	$ 18.7

Organization and Basis of Pre38

Organization and Basis of Presentation Prior period adjustments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Prior Period Adjustments [Line Items]
Cash outflow for shares related to tax withholdings			$ 4,879	$ 45,728
Development service fee expense	$ 23,665	$ 0	$ 52,497	0
Other Income [Member] | Scenario, Previously Reported [Member]
Prior Period Adjustments [Line Items]
Development service fee income		1,219		3,789
General and Administrative Expense [Member] | Scenario, Previously Reported [Member]
Prior Period Adjustments [Line Items]
Development service fee expense		$ 1,058		3,210
Accounting Standards Update 2016-09 [Member] | Scenario, Previously Reported [Member]
Prior Period Adjustments [Line Items]
Cash outflow for shares related to tax withholdings				$ 4,800

Income per Common Share of th39

Income per Common Share of the Trust (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income (Numerator) [Abstract]
Net income available to common shareholders	$ 59,539	$ 54,253	$ 153,982	$ 161,434
Weighted Average Shares (Denominator) [Abstract]
Weighted Average Number of Shares Outstanding, Basic	146,811	146,215	146,678	146,121
Dilutive shares for long-term compensation plans	785	892	752	667
Weighted Average Number of Shares Outstanding, Diluted	147,596	147,107	147,430	146,788
Common shares [Member]
Earnings Per Share, Basic [Abstract]
Income per common share - basic	$ 0.41	$ 0.37	$ 1.05	$ 1.10
Earnings Per Share, Diluted [Abstract]
Income per common share - diluted	$ 0.40	$ 0.37	$ 1.04	$ 1.10

Income per Common Share of th40

Income per Common Share of the Trust Income per Common Share of the Trust - Anti-dilutive Options (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock Option [Member]
Antidilutive Options Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Options Excluded from Computation of Earnings Per Share	0	160,000	0	762,000

Income per Common Share of th41

Income per Common Share of the Trust - Options Exercised (Details) - shares	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Stock Option [Member] | Common shares [Member]
Stock Option Exercises [Line Items]
Amount of Options Exercises in Period	79,000	167,000	369,000

Income per Common Share of th42

Income per Common Share of the Trust - Share Repurchase (Details) - Common shares [Member] - 2015 Share Repurchase Program [Member] $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017USD ($)shares	Sep. 30, 2017USD ($)shares
Class of Stock [Line Items]
Authorized amount of shares available to be repurchased under a share repurchase plan | $	$ 250	$ 250
Number of shares repurchased during period | shares	0	0

Income per Common Unit of the43

Income per Common Unit of the Operating Partnership - Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income (Numerator) [Abstract]
Net income available to common shareholders	$ 59,539	$ 54,253	$ 153,982	$ 161,434
Weighted Average Units (Denominator) [Abstract]
Weighted Average Number of Shares Outstanding, Basic	146,811	146,215	146,678	146,121
Dilutive units for long-term compensation plans	785	892	752	667
Weighted Average Number of Shares Outstanding, Diluted	147,596	147,107	147,430	146,788
Liberty Property Limited Partnership [Member]
Income (Numerator) [Abstract]
Income from continuing operations net of noncontrolling interest - consolidated joint ventures	$ 61,084	$ 55,677	$ 158,026	$ 165,684
Less: Preferred unit distributions	(118)	(118)	(354)	(354)
Net income available to common shareholders	$ 60,966	$ 55,559	$ 157,672	$ 165,330
Weighted Average Units (Denominator) [Abstract]
Weighted Average Number of Shares Outstanding, Basic	150,339	149,751	150,206	149,659
Dilutive units for long-term compensation plans	785	892	752	667
Weighted Average Number of Shares Outstanding, Diluted	151,124	150,643	150,958	150,326
Liberty Property Limited Partnership [Member] | Common Units [Member]
Earnings Per Unit, Basic [Abstract]
Income per common share - basic	$ 0.41	$ 0.37	$ 1.05	$ 1.10
Earnings Per Unit, Diluted [Abstract]
Income per common share - diluted	$ 0.40	$ 0.37	$ 1.04	$ 1.10

Income per Common Unit of the44

Income per Common Unit of the Operating Partnership - Anti-dilutive Options (Details) - Stock Option [Member] - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Options Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Options Excluded from Computation of Earnings Per Share	0	160,000	0	762,000
Liberty Property Limited Partnership [Member]
Antidilutive Options Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Options Excluded from Computation of Earnings Per Share	0	160,000	0	762,000

Income per Common Unit of the45

Income per Common Unit of the Operations Partnership - Options Exercised (Details) - shares	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Liberty Property Limited Partnership [Member] | Stock Option [Member] | Common Units [Member]
Stock Option Exercises [Line Items]
Amount of Options Exercises in Period	79,000	167,000	369,000

Income per Common Unit of the46

Income per Common Unit of the Operating Partnership - Unit Repurchase (Details) - 2015 Share Repurchase Program [Member] $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017USD ($)shares	Sep. 30, 2017USD ($)shares
Common shares [Member]
Class of Stock [Line Items]
Authorized amount of shares available to be repurchased under a share repurchase plan | $	$ 250	$ 250
Number of units repurchased during period | shares	0	0
Liberty Property Limited Partnership [Member] | Common Units [Member]
Class of Stock [Line Items]
Authorized amount of shares available to be repurchased under a share repurchase plan | $	$ 250	$ 250
Number of units repurchased during period | shares	0	0

Accumulated Other Comprehensi47

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance		$ 3,062,923
Ending Balance		3,071,997
Total accumulated other comprehensive loss		3,062,923		$ 3,071,997	$ 3,062,923
Total accumulated other comprehensive loss included in shareholders' equity/owners' equity				3,012,814	3,003,391
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance		(56,767)	$ (22,023)
Unrealized income (loss)		16,314	(23,003)
Ending Balance		(40,453)	(45,026)
Total accumulated other comprehensive loss		(56,767)	(22,023)	(40,453)	(56,767)	$ (45,026)
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance		(455)	(865)
Unrealized income (loss)		(25)	(1,955)
Reclassification adjustment	[1]	391	823
Ending Balance		(89)	(1,997)
Total accumulated other comprehensive loss		(455)	(865)	(89)	(455)	(1,997)
AOCI Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Ending Balance		(40,542)	(47,023)
Total accumulated other comprehensive loss		(40,542)	(47,023)	(40,542)		(47,023)
AOCI Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Ending Balance		801	951
Total accumulated other comprehensive loss		801	$ 951	801		951
AOCI Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance		(56,031)
Ending Balance		(39,741)
Total accumulated other comprehensive loss		$ (56,031)		(39,741)	$ (56,031)
Total accumulated other comprehensive loss included in shareholders' equity/owners' equity				$ (39,741)		$ (46,072)
[1]	Amounts reclassified out of Accumulated Other Comprehensive Loss/General & Limited Partner's Equity into contractual interest expense.

Assets Held for Sale (Details)

Assets Held for Sale (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017USD ($)abldg	Sep. 30, 2017USD ($)abldg	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Assets Held for Sale [Line Items]
Gross Proceeds		$ 56,474	$ 142,808
Assets held for sale	$ 177,549	$ 177,549		$ 4,548
Lehigh Central PA [Member] | 2017 held for sale [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Assets Held for Sale [Line Items]
Gross Proceeds	$ 249,000
Number of Real Estate Properties | bldg	2	2
Leaseable square feet | a	1,700,000	1,700,000
Acres of developable land | a	44	44
Chicago Minneapolis [Member] | 2017 held for sale [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Assets Held for Sale [Line Items]
Acres of developable land | a	9	9
Land, Buildings and Improvements [Member] | Lehigh Central PA [Member] | 2017 held for sale [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Assets Held for Sale [Line Items]
Assets held for sale	$ 176,400	$ 176,400
Land and Land Improvements [Member] | Chicago Minneapolis [Member] | 2017 held for sale [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Assets Held for Sale [Line Items]
Assets held for sale	$ 1,100	$ 1,100

Building Acquisitions and Dispo

Building Acquisitions and Dispositions (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)ft²abldg	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)ft²abldg	Sep. 30, 2016USD ($)
Property, Plant and Equipment [Line Items]
Gross Proceeds			$ 56,474	$ 142,808
Gain on property dispositions	$ 23,840	$ 1,318	$ 30,542	$ 25,671
2015 sales [Member]
Property, Plant and Equipment [Line Items]
Gain on property dispositions	$ 14,300
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	6		6
Leaseable square feet | ft²	260,018		260,018
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	53		53
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds			$ 48,901
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Chicago Minneapolis [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	3		3
Leaseable square feet | ft²	136,110		136,110
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Chicago Minneapolis [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Chicago Minneapolis [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds			$ 8,917
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Florida [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Florida [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	16		16
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Florida [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds			$ 13,256
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Houston [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Houston [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	26		26
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Houston [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds			$ 4,270
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Philadelphia [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Philadelphia [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	2		2
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Philadelphia [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds			$ 6,904
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Southeastern PA [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	3		3
Leaseable square feet | ft²	123,908		123,908
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Southeastern PA [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	3		3
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Southeastern PA [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds			$ 11,815
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Other Segments [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Other Segments [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	6		6
Disposal Group, Not Discontinued Operations [Member] | 2017 sales [Member] | Operating Segments [Member] | Other Segments [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds			$ 3,739
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	3		3
Leaseable square feet | ft²	133,489		133,489
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	24		24
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds	$ 21,477
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Chicago Minneapolis [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	2		2
Leaseable square feet | ft²	104,994		104,994
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Chicago Minneapolis [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Chicago Minneapolis [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds	$ 5,817
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Florida [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Florida [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	5		5
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Florida [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds	$ 10,620
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Houston [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Houston [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	19		19
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Houston [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds	$ 2,275
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Philadelphia [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Philadelphia [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Philadelphia [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds	$ 0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Southeastern PA [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	1		1
Leaseable square feet | ft²	28,495		28,495
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Southeastern PA [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Southeastern PA [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds	$ 2,765
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Other Segments [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Other Segments [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
Disposal Group, Not Discontinued Operations [Member] | 2017 sales current quarter [Member] | Operating Segments [Member] | Other Segments [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Gross Proceeds	$ 0
2017 acquisitions current quarter [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	3		3
Leaseable square feet | ft²	354,391		354,391
2017 acquisitions current quarter [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions current quarter [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price	$ 42,249
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Carolinas Richmond [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Carolinas Richmond [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Carolinas Richmond [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price	$ 0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Lehigh Central PA [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Lehigh Central PA [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Lehigh Central PA [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price	$ 0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | United Kingdom [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | United Kingdom [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | United Kingdom [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price	$ 0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Arizona [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Arizona [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Arizona [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price	$ 0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Atlanta [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Atlanta [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Atlanta [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price	$ 0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | DC Metro [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | DC Metro [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | DC Metro [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price	$ 0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | New Jersey [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	2		2
Leaseable square feet | ft²	205,116		205,116
2017 acquisitions current quarter [Member] | Operating Segments [Member] | New Jersey [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | New Jersey [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price	$ 25,599
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Southern California [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	1		1
Leaseable square feet | ft²	149,275		149,275
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Southern California [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions current quarter [Member] | Operating Segments [Member] | Southern California [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price	$ 16,650
2017 acquisitions [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	4		4
Leaseable square feet | ft²	454,971		454,971
2017 acquisitions [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	254		254
2017 acquisitions [Member] | Southern California [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price			$ 101,349
2017 acquisitions [Member] | Operating Segments [Member] | Carolinas Richmond [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions [Member] | Operating Segments [Member] | Carolinas Richmond [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	11		11
2017 acquisitions [Member] | Operating Segments [Member] | Carolinas Richmond [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price			$ 1,242
2017 acquisitions [Member] | Operating Segments [Member] | Lehigh Central PA [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions [Member] | Operating Segments [Member] | Lehigh Central PA [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	95		95
2017 acquisitions [Member] | Operating Segments [Member] | Lehigh Central PA [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price			$ 17,798
2017 acquisitions [Member] | Operating Segments [Member] | United Kingdom [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions [Member] | Operating Segments [Member] | United Kingdom [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	35		35
2017 acquisitions [Member] | Operating Segments [Member] | United Kingdom [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price			$ 12,550
2017 acquisitions [Member] | Operating Segments [Member] | Arizona [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions [Member] | Operating Segments [Member] | Arizona [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	6		6
2017 acquisitions [Member] | Operating Segments [Member] | Arizona [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price			$ 1,327
2017 acquisitions [Member] | Operating Segments [Member] | Atlanta [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions [Member] | Operating Segments [Member] | Atlanta [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	80		80
2017 acquisitions [Member] | Operating Segments [Member] | Atlanta [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price			$ 2,867
2017 acquisitions [Member] | Operating Segments [Member] | DC Metro [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	0		0
Leaseable square feet | ft²	0		0
2017 acquisitions [Member] | Operating Segments [Member] | DC Metro [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	10		10
2017 acquisitions [Member] | Operating Segments [Member] | DC Metro [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price			$ 504
2017 acquisitions [Member] | Operating Segments [Member] | New Jersey [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	2		2
Leaseable square feet | ft²	205,116		205,116
2017 acquisitions [Member] | Operating Segments [Member] | New Jersey [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	17		17
2017 acquisitions [Member] | Operating Segments [Member] | New Jersey [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price			$ 29,301
2017 acquisitions [Member] | Operating Segments [Member] | Southern California [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Number of Real Estate Properties | bldg	2		2
Leaseable square feet | ft²	249,855		249,855
2017 acquisitions [Member] | Operating Segments [Member] | Southern California [Member] | Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Acres of developable land | a	0		0
2017 acquisitions [Member] | Operating Segments [Member] | Southern California [Member] | Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Purchase price			$ 35,760

Segment Information - Income St

Segment Information - Income Statement (Details) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Operating revenue		$ 193,653,000	$ 190,857,000	$ 552,149,000	$ 567,653,000
Net operating income		54,875,000	75,322,000	176,941,000	204,098,000
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Interest expense		(23,060,000)	(29,528,000)	(67,345,000)	(91,071,000)
Loss on debt extinguishment		0	(3,494,000)	0	(3,494,000)
Depreciation and amortization expense		(46,582,000)	(46,920,000)	(137,831,000)	(154,543,000)
Impairment charges - real estate assets		(9,650,000)	0	(9,650,000)	0
Gain on property dispositions		23,840,000	1,318,000	30,542,000	25,671,000
Equity in earnings of unconsolidated joint ventures		4,305,000	9,043,000	14,026,000	19,540,000
General and administrative expense		(11,910,000)	(15,379,000)	(43,949,000)	(51,888,000)
Expensed pursuit costs		(4,772,000)	(772,000)	(4,957,000)	(882,000)
Income taxes		(582,000)	(80,000)	(1,528,000)	(1,633,000)
Net income		61,159,000	55,734,000	158,221,000	165,854,000
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenue		0	0	0	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenue		169,614,000	191,033,000	498,247,000	567,994,000
Net operating income		113,718,000	125,254,000	331,446,000	365,428,000
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenue		(137,000)	(176,000)	(18,000)	(341,000)
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Interest expense		(23,060,000)	(29,528,000)	(67,345,000)	(91,071,000)
Loss on debt extinguishment		0	(3,494,000)	0	(3,494,000)
Depreciation and amortization expense	[1]	(33,521,000)	(34,896,000)	(99,829,000)	(113,855,000)
Impairment charges - real estate assets		(9,650,000)	0	(9,650,000)	0
Gain on property dispositions		23,840,000	1,318,000	30,542,000	25,671,000
Equity in earnings of unconsolidated joint ventures		4,305,000	9,043,000	14,026,000	19,540,000
General and administrative expense	[1]	(8,104,000)	(10,406,000)	(31,230,000)	(33,910,000)
Expensed pursuit costs		(4,772,000)	(772,000)	(4,957,000)	(882,000)
Income taxes	[1]	(64,000)	17,000	(240,000)	(1,203,000)
Other		(1,533,000)	(802,000)	(4,542,000)	(370,000)
Development Service Fee Income [Member] | Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Operating revenue		24,176,000	0	53,920,000	0
Carolinas Richmond [Member] | Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue		18,910,000	17,292,000	55,192,000	49,226,000
Net operating income		13,621,000	12,198,000	39,698,000	34,257,000
Chicago Minneapolis [Member] | Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue		16,147,000	23,417,000	47,789,000	66,848,000
Net operating income		9,554,000	12,519,000	28,913,000	35,761,000
Florida [Member] | Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue		15,072,000	28,115,000	43,802,000	85,230,000
Net operating income		10,176,000	18,340,000	29,686,000	53,129,000
Houston [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Impairment charges - real estate assets		(9,700,000)		(9,700,000)
Houston [Member] | Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue		15,167,000	14,870,000	44,720,000	43,840,000
Net operating income		8,701,000	7,989,000	23,263,000	24,858,000
Lehigh Central PA [Member] | Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue		40,698,000	34,157,000	122,048,000	102,182,000
Net operating income		29,995,000	24,982,000	88,656,000	73,939,000
Philadelphia [Member] | Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue		11,137,000	10,513,000	33,501,000	31,253,000
Net operating income		8,743,000	7,750,000	25,987,000	23,089,000
Southeastern PA [Member] | Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue		15,422,000	24,563,000	45,165,000	74,789,000
Net operating income		9,246,000	16,244,000	25,866,000	44,544,000
United Kingdom [Member] | Operating Segments [Member] | UNITED KINGDOM
Segment Reporting Information [Line Items]
Operating revenue		3,773,000	3,275,000	10,204,000	10,352,000
Net operating income		1,781,000	2,031,000	5,288,000	6,871,000
Other Segments [Member] | Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue		33,288,000	34,831,000	95,826,000	104,274,000
Net operating income		$ 21,901,000	$ 23,201,000	$ 64,089,000	$ 68,980,000
[1]	Excludes costs which are included in determining SNOI.

Segment Information - Total Ass

Segment Information - Total Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Assets	$ 6,309,674	$ 5,992,813
Operating Segments [Member]
Segment Reporting Information [Line Items]
Assets	6,240,009	5,889,764
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Assets	69,665	103,049
North America [Member] | Operating Segments [Member] | Carolinas Richmond [Member]
Segment Reporting Information [Line Items]
Assets	518,279	503,920
North America [Member] | Operating Segments [Member] | Chicago Minneapolis [Member]
Segment Reporting Information [Line Items]
Assets	611,656	616,298
North America [Member] | Operating Segments [Member] | Florida [Member]
Segment Reporting Information [Line Items]
Assets	518,169	514,431
North America [Member] | Operating Segments [Member] | Houston [Member]
Segment Reporting Information [Line Items]
Assets	514,622	530,438
North America [Member] | Operating Segments [Member] | Lehigh Central PA [Member]
Segment Reporting Information [Line Items]
Assets	1,372,896	1,311,815
North America [Member] | Operating Segments [Member] | Philadelphia [Member]
Segment Reporting Information [Line Items]
Assets	651,108	557,510
North America [Member] | Operating Segments [Member] | Southeastern PA [Member]
Segment Reporting Information [Line Items]
Assets	256,378	262,155
North America [Member] | Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Assets	1,563,244	1,403,431
UNITED KINGDOM | Operating Segments [Member] | United Kingdom [Member]
Segment Reporting Information [Line Items]
Assets	$ 233,657	$ 189,766

Accounting for the Impairment52

Accounting for the Impairment of Long-Lived Assets and Fee Development Contracts (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Impairment charges - real estate assets	$ 9,650,000	$ 0	$ 9,650,000	$ 0
Loss on fee development contracts	0	0	0	0
Expensed pursuit costs	4,772,000	$ 772,000	4,957,000	$ 882,000
Houston [Member]
Property, Plant and Equipment [Line Items]
Impairment charges - real estate assets	$ 9,700,000		$ 9,700,000

Noncontrolling Interests of t53

Noncontrolling Interests of the Trust- Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Redeemable Noncontrolling Interest [Line Items]
Limited Partners' common units outstanding	3,528,281	3,530,031
Liberty Property Limited Partnership [Member]
Redeemable Noncontrolling Interest [Line Items]
Limited Partners' common units outstanding	3,528,281	3,530,031
Market value of common units based on closing price	$ 144.9

Limited Partners' Equity of t54

Limited Partners' Equity of the Operating Partnership - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Limited Partners' Capital Account [Line Items]
Limited Partners' common units outstanding	3,528,281	3,530,031
Liberty Property Limited Partnership [Member]
Limited Partners' Capital Account [Line Items]
Limited Partners' common units outstanding	3,528,281	3,530,031
Market value of common units based on closing price	$ 144.9

Noncontrolling Interest - Ope55

Noncontrolling Interest - Operating Partnership/Limited Partners' Equity - Preferred Units (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Temporary Equity [Line Items]
Noncontrolling interest - operating partnership - 301,483 preferred units outstanding as of September 30, 2017 and December 31, 2016	$ 7,537	$ 7,537
Series I 2 [Member]
Temporary Equity [Line Items]
Noncontrolling interest - operating partnership - 301,483 preferred units outstanding as of September 30, 2017 and December 31, 2016	$ 7,537
Units	301,483	301,483
Liquidation Preference	$ 25
Dividend Rate	6.25%

Disclosure of Fair Value of F56

Disclosure of Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	$ 269,380	$ 276,650
Unsecured Debt	2,282,828	2,280,286
Unsecured Debt [Member] | Fair Value, Inputs, Level 3 [Member] | Long-term Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	2,379,014	2,340,762
Mortgage Loans | Fair Value, Inputs, Level 3 [Member] | Long-term Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	$ 281,671	$ 286,684

Unconsolidated Joint Ventures (

Unconsolidated Joint Ventures (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)ft²bldg	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)ft²bldg	Sep. 30, 2016USD ($)
Cambridge Medipark Ltd [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	50.00%		50.00%
Liberty Property 19th & Arch [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	20.00%		20.00%
Joint venture, 2017 sales current quarter [Member] | Gain on equity method investments [Member] | Cambridge Medipark Ltd [Member] | Disposal Group, Not Discontinued Operations [Member] | Leaseholds and Leasehold Improvements [Member]
Schedule of Equity Method Investments [Line Items]
Gain (loss) on sale of leasehold interests	$ 1.3
Joint venture, 2017 sales [Member] | Gain on equity method investments [Member] | Cambridge Medipark Ltd [Member] | Disposal Group, Not Discontinued Operations [Member] | Leaseholds and Leasehold Improvements [Member]
Schedule of Equity Method Investments [Line Items]
Gain (loss) on sale of leasehold interests			$ 5.8
Joint venture, 2016 sales current quarter [Member] | Gain on equity method investments [Member] | Cambridge Medipark Ltd [Member] | Disposal Group, Not Discontinued Operations [Member] | Leaseholds and Leasehold Improvements [Member]
Schedule of Equity Method Investments [Line Items]
Gain (loss) on sale of leasehold interests		$ 3.3
Joint venture, 2016 sales [Member] | Gain on equity method investments [Member] | Cambridge Medipark Ltd [Member] | Disposal Group, Not Discontinued Operations [Member] | Leaseholds and Leasehold Improvements [Member]
Schedule of Equity Method Investments [Line Items]
Gain (loss) on sale of leasehold interests				$ 3.5
Joint venture, 2017 acquisitions current quarter [Member] | Liberty Property 19th & Arch [Member] | Building and Building Improvements [Member]
Schedule of Equity Method Investments [Line Items]
Leaseable square feet | ft²	48,031		48,031
Number of Real Estate Properties | bldg	1		1
Purchase price	$ 15

Derivative Instruments (Details

Derivative Instruments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Interest Rate Derivatives [Abstract]
Number of interest rate swap contracts	3		3
aggregate notional amount	$ 96,900		$ 96,900		$ 98,900
Termination value of interest rate swap, including accrued interest	3,100		3,100
Interest Rate Cash Flow Hedges [Abstract]
Fair value of interest rate swaps	3,100		3,100		$ 4,900
Amount estimated to be reclassified from accumulated other comprehensive income as an increase to interest expense	200		200
Interest Rate Swap [Member] | Other Comprehensive Income (Loss) [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) related to the effective portion recognized in other comprehensive income (loss)	19	$ 415	(7)	$ (1,928)
Interest Rate Swap [Member] | Interest Expense [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of loss related to the effective portion subsequently reclassified to interest expense	(75)	(264)	(391)	(823)
Amount of (loss) gain related to the ineffective portion recognized in interest expense	$ (8)	$ 7	$ 5	$ (71)

Commitments and Contingencies -

Commitments and Contingencies - Future Minimum Rental Payments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
2017 (remaining)	$ 443,000		$ 443,000
2,018	1,767,000		1,767,000
2,019	1,767,000		1,767,000
2,020	1,767,000		1,767,000
2,021	1,767,000		1,767,000
2022 and thereafter	34,905,000		34,905,000
Total	42,416,000		42,416,000
Other Expenses [Abstract]
Operating ground lease expense	$ 313,000	$ 241,000	$ 936,000	$ 734,000

Commitments and Contingencies60

Commitments and Contingencies - Loss Contingencies (Details) $ in Millions	Sep. 30, 2017USD ($)
Legal Matters [Abstract]
Loss Contingency, Pending Claims, Number	0
Other [Abstract]
Letter of credit obligations	$ 6.3

Commitments and Contingencies61

Commitments and Contingencies - Supply Commitments (Details) $ in Thousands, ft² in Millions	9 Months Ended
	Sep. 30, 2017USD ($)ft²propertiesbldg	Dec. 31, 2016USD ($)
Supply Commitment [Line Items]
Development in progress	$ 395,089	$ 267,450
Building and Building Improvements [Member] | American Water Works, Inc [Member]
Supply Commitment [Line Items]
Fee development commitment	170,100
Costs incurred to date	71,800
Supply Commitment [Member] | Construction in Progress [Member]
Supply Commitment [Line Items]
Deferred leasing costs in development	$ 14,400
Construction in Progress [Member]
Supply Commitment [Line Items]
Leaseable square feet | ft²	5.9
Number of Real Estate Properties | properties	24
Total anticipated development cost	$ 560,800
Buildings and land parcels [Member]
Supply Commitment [Line Items]
Remaining amount committed or obligated to pay	8,300
Tenant Improvements [Member]
Supply Commitment [Line Items]
Tenant improvements not yet completed	$ 26,700
Equity Method Investments [Member] | Supply Commitment [Member] | Construction in Progress [Member]
Supply Commitment [Line Items]
Number of Real Estate Properties | bldg	4
Remaining amount committed or obligated to pay	$ 976,900

Commitments and Contingencies62

Commitments and Contingencies - Purchase Commitments (Details) $ in Millions	Sep. 30, 2017USD ($)
Land and Land Improvements [Member] | Land Purchases [Member]
Long-term Purchase Commitment [Line Items]
Remaining amount committed to future acquisitions	$ 35.6

Supplemental Disclosure to St63

Supplemental Disclosure to Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Supplemental Cash Flow Information [Abstract]
Write-off of fully depreciated/amortized property and deferred costs	$ 26,609	$ 26,349
Write-off of depreciated/amortized property and deferred costs due to sale	13,127	34,513
Write-off of costs related to early debt extinguishment	0	109
Redemption of noncontrolling interests - common units	27	132
Unrealized gain (loss) on cash flow hedge	366	(1,132)
Changes in accrued development capital expenditures	18,255	(7,522)
Capitalized equity-based compensation	$ 877	$ 980

Subsequent Events (Details)

Subsequent Events (Details) $ in Thousands	Oct. 02, 2017USD ($)ft²bldg	Oct. 31, 2017	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Oct. 01, 2017USD ($)
Agreement of Sale
Gross Proceeds			$ 56,474	$ 142,808
Subsequent Event [Member]
Credit Facility
debt issuance costs					$ 5,100
Subsequent Event [Member] | 2017 subsequent event [Member] | Southeastern PA [Member]
Agreement of Sale
Number of Real Estate Properties | bldg	14
square feet | ft²	641,000
Gross Proceeds	$ 75,400
Subsequent Event [Member] | 2014 Credit Facility [Member] | Line of Credit [Member]
Credit Facility
maximum borrowing capacity					800,000
Subsequent Event [Member] | 2017 Credit Facility [Member] | Line of Credit [Member]
Credit Facility
maximum borrowing capacity					900,000
length of maturity extension		1 year
annual facility fee		0.15%
Subsequent Event [Member] | 2017 Credit Facility [Member] | Revolving Credit Facility [Member]
Credit Facility
maximum borrowing capacity					800,000
basis spread on variable rate		0.875%
competitive bid option, percentage of facility		50.00%
Subsequent Event [Member] | 2017 Credit Facility [Member] | Commercial Paper [Member]
Credit Facility
maximum borrowing capacity					$ 100,000
basis spread on variable rate		0.95%