Liberty Property Trust (LPT) 10-Q 30 Oct 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information Document	9 Months Ended
	Sep. 30, 2014	Oct. 27, 2014
Entity Information [Line Items]	'	'
Entity Registrant Name	'LIBERTY PROPERTY TRUST	'
Entity Central Index Key	'0000921112	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	148,545,996
Liberty Property Limited Partnership [Member]	'	'
Entity Information [Line Items]	'	'
Entity Registrant Name	'LIBERTY PROPERTY LIMITED PARTNERSHIP	'
Entity Central Index Key	'0000921113	'

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2014	Dec. 31, 2013
ASSETS	'	'
Land and land improvements	$1,195,924,000	$1,138,922,000
Building and improvements	5,413,512,000	5,142,480,000
Less accumulated depreciation	-1,177,726,000	-1,057,644,000
Operating real estate	5,431,710,000	5,223,758,000
Development in progress	250,506,000	209,187,000
Land held for development	265,864,000	233,055,000
Net real estate	5,948,080,000	5,666,000,000
Cash and cash equivalents	39,086,000	163,414,000
Restricted cash	22,918,000	51,456,000
Accounts receivable	18,571,000	13,900,000
Deferred rent receivable	111,823,000	99,956,000
Deferred financing and leasing costs, net of accumulated amortization (2014, $167,045; 2013, $140,933)	217,261,000	226,377,000
Investments in and advances to unconsolidated joint ventures	202,570,000	179,655,000
Assets held for sale	2,895,000	278,962,000
Prepaid expenses and other assets	97,638,000	95,840,000
Total assets	6,660,842,000	6,775,560,000
LIABILITIES	'	'
Mortgage loans	534,547,000	545,306,000
Unsecured notes	2,508,886,000	2,708,213,000
Credit facility	140,950,000	0
Accounts payable	65,668,000	70,406,000
Accrued interest	41,277,000	25,777,000
Dividend and distributions payable	72,046,000	71,323,000
Other liabilities	221,943,000	250,819,000
Total liabilities	3,585,317,000	3,671,844,000
Noncontrolling interest - operating partnership - 301,483 preferred units outstanding as of September 30, 2014 and December 31, 2013	7,537,000	7,537,000
EQUITY	'	'
Common shares of beneficial interest, $.001 par value, 283,987,000 shares authorized; 149,354,294 (includes 1,249,909 in treasury) and 147,846,801 (includes 1,249,909 in treasury) shares issued and outstanding as of September 30, 2014 and December 31, 2013, respectively	149,000	148,000
Additional paid-in capital	3,724,184,000	3,669,618,000
Accumulated other comprehensive loss	3,707,000	9,742,000
Distributions in excess of net income	-666,646,000	-591,713,000
Common shares in treasury, at cost, 1,249,909 shares as of September 30, 2014 and December 31, 2013	-51,951,000	-51,951,000
Total Liberty Property Trust shareholders' equity	3,009,443,000	3,035,844,000
Noncontrolling interest - operating partnership	'	'
Noncontrolling interest - operating partnerships	54,626,000	56,713,000
Noncontrolling interest - consolidated joint ventures	3,919,000	3,622,000
Total equity	3,067,988,000	3,096,179,000
Total liabilities, noncontrolling interest - operating partnership and equity	6,660,842,000	6,775,560,000
Liberty Property Limited Partnership [Member]	'	'
ASSETS	'	'
Land and land improvements	1,195,924,000	1,138,922,000
Building and improvements	5,413,512,000	5,142,480,000
Less accumulated depreciation	-1,177,726,000	-1,057,644,000
Operating real estate	5,431,710,000	5,223,758,000
Development in progress	250,506,000	209,187,000
Land held for development	265,864,000	233,055,000
Net real estate	5,948,080,000	5,666,000,000
Cash and cash equivalents	39,086,000	163,414,000
Restricted cash	22,918,000	51,456,000
Accounts receivable	18,571,000	13,900,000
Deferred rent receivable	111,823,000	99,956,000
Deferred financing and leasing costs, net of accumulated amortization (2014, $167,045; 2013, $140,933)	217,261,000	226,377,000
Investments in and advances to unconsolidated joint ventures	202,570,000	179,655,000
Assets held for sale	2,895,000	278,962,000
Prepaid expenses and other assets	97,638,000	95,840,000
Total assets	6,660,842,000	6,775,560,000
LIABILITIES	'	'
Mortgage loans	534,547,000	545,306,000
Unsecured notes	2,508,886,000	2,708,213,000
Credit facility	140,950,000	0
Accounts payable	65,668,000	70,406,000
Accrued interest	41,277,000	25,777,000
Dividend and distributions payable	72,046,000	71,323,000
Other liabilities	221,943,000	250,819,000
Total liabilities	3,585,317,000	3,671,844,000
Noncontrolling interest - operating partnership - 301,483 preferred units outstanding as of September 30, 2014 and December 31, 2013	7,537,000	7,537,000
EQUITY	'	'
General partner’s equity - 148,104,385 (net of 1,249,909 treasury units) and 146,596,892 (net of 1,249,909 treasury units) common units outstanding as of September 30, 2014 and December 31, 2013, respectively	3,009,443,000	3,035,844,000
Limited partners' equity	54,626,000	56,713,000
Noncontrolling interest - operating partnership	'	'
Noncontrolling interest - consolidated joint ventures	3,919,000	3,622,000
Total equity	3,067,988,000	3,096,179,000
Total liabilities, noncontrolling interest - operating partnership and equity	$6,660,842,000	$6,775,560,000

Balance_Sheet_Parenthetical_Pa

Balance Sheet Parenthetical (Parentheticals) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Amortized Cost on Deferred Financing and Leasing Costs	$167,045,000	$140,933,000
Noncontrolling Interest Operating Partnership Common Units Outstanding	3,553,566	3,556,556
Common Stock, Par or Stated Value Per Share	$0.00	$0.00
Common Stock, Shares Authorized	283,987,000	183,987,000
Common Stock, Shares, Issued	149,354,294	147,846,801
Common Stock, Shares, Outstanding	149,354,294	147,846,801
Treasury Stock, Shares	1,249,909	1,249,909
Liberty Property Limited Partnership [Member]	'	'
Amortized Cost on Deferred Financing and Leasing Costs	$167,045,000	$140,933,000
Limited Partners' Capital Account, Units Outstanding	3,553,566	3,556,556
Common Stock, Shares, Outstanding	148,104,385	146,596,892
Treasury Stock, Shares	1,249,909	1,249,909
Series I 2 [Member]	'	'
Temporary Equity, Shares Outstanding	301,483	301,483
Series I 2 [Member] | Liberty Property Limited Partnership [Member]	'	'
Temporary Equity, Shares Outstanding	301,483	301,483

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
OPERATING REVENUE	'	'	'	'
Rental	$143,294	$110,260	$421,620	$321,932
Operating expense reimbursement	55,062	45,088	167,326	131,566
Total operating revenue	198,356	155,348	588,946	453,498
OPERATING EXPENSE	'	'	'	'
Rental property	33,105	27,634	103,728	79,547
Real estate taxes	25,595	18,925	75,812	55,788
General and administrative	14,748	17,217	48,077	53,466
Depreciation and amortization	58,578	39,159	173,184	113,906
Total operating expenses	132,026	102,935	400,801	302,707
Operating income	66,330	52,413	188,145	150,791
OTHER INCOME (EXPENSE)	'	'	'	'
Other income	6,230	4,512	11,785	14,269
Interest expense	-37,958	-33,542	-115,635	-89,414
Total other income (expense)	-31,728	-29,030	-103,850	-75,145
Income before (loss) gain on property dispositions, income taxes and equity in earnings of unconsolidated joint ventures	34,602	23,383	84,295	75,646
(Loss) gain on property dispositions	-20	0	1,879	0
Income taxes	-859	-629	-2,083	-1,780
Equity in earnings of unconsolidated joint ventures	1,592	650	7,297	3,973
Income from continuing operations	35,315	23,404	91,388	77,839
Discontinued operations (including net gain on property dispositions of $38 and $29 for the quarters ended September 30, 2014 and 2013, respectively and $46,291 and $49,367 for the nine month periods ended September 30, 2014 and 2013, respectively)	136	6,544	48,276	70,008
Net income	35,451	29,948	139,664	147,847
Noncontrolling interest – operating partnership	-944	-843	-3,618	-7,394
Noncontrolling interest - consolidated joint ventures	-84	-406	-474	-406
Net income available to common shareholders	34,423	28,699	135,572	140,047
Comprehensive income attributable to common shareholders	'	'	'	'
Net income	35,451	29,948	139,664	147,847
Other comprehensive (loss) income - foreign currency translation	-13,000	4,927	-5,189	115
Other comprehensive income (loss) - change in net unrealized gain on derivative instruments	666	0	-990	0
Other comprehensive (loss) income	-12,334	4,927	-6,179	115
Total comprehensive income	23,117	34,875	133,485	147,962
Less: comprehensive income attributable to noncontrolling interest	-739	-1,370	-3,948	-7,777
Comprehensive income attributable to common shareholders	22,378	33,505	129,537	140,185
Weighted average number of common shares outstanding	'	'	'	'
Basic	147,422	135,628	146,987	124,889
Diluted	148,088	136,328	147,661	125,655
Amounts attributable to common shareholders	'	'	'	'
Income from continuing operations	34,290	22,316	88,430	72,048
Discontinued operations	133	6,383	47,142	67,999
Net income available to common shareholders	34,423	28,699	135,572	140,047
Liberty Property Limited Partnership [Member]	'	'	'	'
OPERATING REVENUE	'	'	'	'
Rental	143,294	110,260	421,620	321,932
Operating expense reimbursement	55,062	45,088	167,326	131,566
Total operating revenue	198,356	155,348	588,946	453,498
OPERATING EXPENSE	'	'	'	'
Rental property	33,105	27,634	103,728	79,547
Real estate taxes	25,595	18,925	75,812	55,788
General and administrative	14,748	17,217	48,077	53,466
Depreciation and amortization	58,578	39,159	173,184	113,906
Total operating expenses	132,026	102,935	400,801	302,707
Operating income	66,330	52,413	188,145	150,791
OTHER INCOME (EXPENSE)	'	'	'	'
Other income	6,230	4,512	11,785	14,269
Interest expense	-37,958	-33,542	-115,635	-89,414
Total other income (expense)	-31,728	-29,030	-103,850	-75,145
Income before (loss) gain on property dispositions, income taxes and equity in earnings of unconsolidated joint ventures	34,602	23,383	84,295	75,646
(Loss) gain on property dispositions	-20	0	1,879	0
Income taxes	-859	-629	-2,083	-1,780
Equity in earnings of unconsolidated joint ventures	1,592	650	7,297	3,973
Income from continuing operations	35,315	23,404	91,388	77,839
Discontinued operations (including net gain on property dispositions of $38 and $29 for the quarters ended September 30, 2014 and 2013, respectively and $46,291 and $49,367 for the nine month periods ended September 30, 2014 and 2013, respectively)	136	6,544	48,276	70,008
Net income	35,451	29,948	139,664	147,847
Noncontrolling interest - consolidated joint ventures	-84	-406	-474	-406
Preferred unit distributions	-118	-118	-354	-2,001
Excess of preferred unit redemption over carrying amount	'	'	0	-1,236
Net income available to common shareholders	35,249	29,424	138,836	144,204
Comprehensive income attributable to common shareholders	'	'	'	'
Net income	35,451	29,948	139,664	147,847
Other comprehensive (loss) income - foreign currency translation	-13,000	4,927	-5,189	115
Other comprehensive income (loss) - change in net unrealized gain on derivative instruments	666	0	-990	0
Other comprehensive (loss) income	-12,334	4,927	-6,179	115
Total comprehensive income	23,117	34,875	133,485	147,962
Weighted average number of common shares outstanding	'	'	'	'
Basic	150,976	139,320	150,541	128,595
Diluted	151,642	140,020	151,215	129,361
Net income allocated to general partners	34,423	28,699	135,572	140,047
Net income allocated to limited partners	944	843	3,618	7,394
Amounts attributable to common shareholders	'	'	'	'
Income from continuing operations	35,231	22,998	90,914	77,433
Net income available to common shareholders	$35,249	$29,424	$138,836	$144,204
Common shares [Member]	'	'	'	'
Basic:	'	'	'	'
Income from continuing operations	$0.23	$0.16	$0.60	$0.58
Income from discontinued operations	$0	$0.05	$0.32	$0.54
Income per common share - basic	$0.23	$0.21	$0.92	$1.12
Diluted:	'	'	'	'
Income from continuing operations	$0.23	$0.16	$0.60	$0.57
Income from discontinued operations	$0	$0.05	$0.32	$0.54
Income per common share - diluted	$0.23	$0.21	$0.92	$1.11
Distributions per common share or unit	$0.48	$0.48	$1.43	$1.43
Common Units [Member] | Liberty Property Limited Partnership [Member]	'	'	'	'
Basic:	'	'	'	'
Income from continuing operations	$0.23	$0.16	$0.60	$0.58
Income from discontinued operations	$0	$0.05	$0.32	$0.54
Income per common share - basic	$0.23	$0.21	$0.92	$1.12
Diluted:	'	'	'	'
Income from continuing operations	$0.23	$0.16	$0.60	$0.57
Income from discontinued operations	$0	$0.05	$0.32	$0.54
Income per common share - diluted	$0.23	$0.21	$0.92	$1.11
Distributions per common share or unit	$0.48	$0.48	$1.43	$1.43

Income_Statement_Parenthetical

Income Statement Parenthetical (Parentheticals) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Gain on property dispositions	$38	$29	$46,291	$49,367
Liberty Property Limited Partnership [Member]	'	'	'	'
Gain on property dispositions	$38	$29	$46,291	$49,367

Consolidated_Statement_of_Equi

Consolidated Statement of Equity (USD $)

Total

Common Shares Of Beneficial Interest [Member]

Additional Paid-In Capital [Member]

Accumulated Other Comprehensive Income [Member]

Distributions in Excess of Net Income [Member]

Common Shares Held in Treasury [Member]

Total Liberty Property Trust Shareholders' Equity [Member]

Noncontrolling interest operating partnership-Common [Member]

Noncontrolling interest operating partnership-Preferred [Member]

Noncontrolling interest-consolidated joint ventures [Member]

Liberty Property Limited Partnership [Member]

Liberty Property Limited Partnership [Member]

Liberty Property Limited Partnership [Member]

Liberty Property Limited Partnership [Member]

Liberty Property Limited Partnership [Member]

General Partners Equity [Member]

Noncontrolling interest operating partnership-Common [Member]

Noncontrolling interest operating partnership-Preferred [Member]

Noncontrolling interest-consolidated joint ventures [Member]

Beginning Balance at Dec. 31, 2013

$3,096,179,000

$148,000

$3,669,618,000

$9,742,000

($591,713,000)

($51,951,000)

$3,035,844,000

$56,713,000

$0

$3,622,000

$3,096,179,000

$3,035,844,000

$56,713,000

$0

$3,622,000

Net proceeds from the issuance of common shares

44,097,000

1,000

44,096,000

'

'

'

44,097,000

'

'

'

'

'

'

'

'

Net income

139,664,000

'

'

'

135,572,000

'

135,572,000

3,264,000

354,000

474,000

139,664,000

135,572,000

3,264,000

354,000

474,000

Redemption of limited partners common units for common shares

'

'

'

'

'

'

'

'

'

'

0

48,000

-48,000

'

'

Contributions from partners

'

'

'

'

'

'

'

'

'

'

54,519,000

54,519,000

'

'

'

Distributions

-216,195,000

'

'

'

-210,505,000

'

-210,505,000

-5,159,000

-354,000

-177,000

'

'

'

'

'

Distributions to partners

'

'

'

'

'

'

'

'

'

'

-216,195,000

-210,505,000

-5,159,000

-354,000

-177,000

Share-based compensation

10,422,000

'

10,422,000

'

'

'

10,422,000

'

'

'

'

'

'

'

'

Other comprehensive (loss) income - foreign currency translation

-5,189,000

'

'

-5,068,000

'

'

-5,068,000

-121,000

'

'

-5,189,000

-5,068,000

-121,000

'

'

Other comprehensive income (loss) - change in net unrealized gain on derivative instruments

-990,000

'

'

-967,000

'

'

-967,000

-23,000

'

'

-990,000

-967,000

-23,000

'

'

Redemption of noncontrolling interests - common units

0

'

48,000

'

'

'

48,000

-48,000

'

'

'

'

'

'

'

Ending Balance at Sep. 30, 2014

3,067,988,000

149,000

3,724,184,000

3,707,000

-666,646,000

-51,951,000

3,009,443,000

54,626,000

0

3,919,000

3,067,988,000

3,009,443,000

54,626,000

0

3,919,000

Beginning Balance at Jun. 30, 2014

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income

35,451,000

'

'

'

'

'

'

'

'

'

35,451,000

'

'

'

'

Other comprehensive (loss) income - foreign currency translation

-13,000,000

'

'

'

'

'

'

'

'

'

-13,000,000

'

'

'

'

Other comprehensive income (loss) - change in net unrealized gain on derivative instruments

666,000

'

'

'

'

'

'

'

'

'

666,000

'

'

'

'

Ending Balance at Sep. 30, 2014

$3,067,988,000

'

'

'

'

($51,951,000)

'

'

'

'

$3,067,988,000

'

'

'

'

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
OPERATING ACTIVITIES	'	'
Net income	$139,664	$147,847
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation and amortization	176,207	137,302
Amortization of deferred financing costs	3,727	2,952
Equity in earnings of unconsolidated joint ventures	-7,297	-3,973
Distributions from unconsolidated joint ventures	0	613
Gain on property dispositions	-48,170	-49,367
Share-based compensation	10,422	8,174
Other	-5,202	-6,248
Changes in operating assets and liabilities:	'	'
Restricted cash	28,469	-2,703
Accounts receivable	-4,771	231
Deferred rent receivable	-11,928	-6,171
Prepaid expenses and other assets	-38,882	-50,389
Accounts payable	18,824	15,494
Accrued interest	15,500	18,922
Other liabilities	-26,232	2,352
Net cash provided by operating activities	250,331	215,036
INVESTING ACTIVITIES	'	'
Investment in operating properties - acquisitions	-97,677	-161,404
Investment in operating properties - other	-61,480	-40,433
Investments in and advances to unconsolidated joint ventures	-13,894	-11,736
Distributions from unconsolidated joint ventures	10,213	6,825
Net proceeds from disposition of properties/land	351,301	134,024
Net proceeds from public reimbursement receivable/escrow	5,501	12,943
Investment in development in progress	-222,484	-81,736
Investment in land held for development	-73,547	-34,642
Investment in deferred leasing costs	-28,409	-22,996
Net cash used in investing activities	-130,476	-199,155
FINANCING ACTIVITIES	'	'
Net proceeds from issuance of common shares	44,097	954,481
Redemption of preferred units	0	-64,500
Proceeds from unsecured notes	0	448,646
Redemption of unsecured notes	-200,000	0
Proceeds from mortgage loans	0	10,401
Repayments of mortgage loans	-9,329	-3,977
Proceeds from credit facility	179,750	344,050
Repayments on credit facility	-38,800	-436,050
Payment of deferred financing costs	-3,622	-3,883
Distribution paid on common shares	-209,779	-170,970
Distribution paid on units/to consolidated joint venture partners	-5,692	-7,619
Net cash (used in) provided by financing activities	-243,375	1,070,579
Net (decrease) increase in cash and cash equivalents	-123,520	1,086,460
Decrease in cash and cash equivalents related to foreign currency translation	-808	-246
Cash and cash equivalents at beginning of period	163,414	38,356
Cash and cash equivalents at end of period	39,086	1,124,570
Liberty Property Limited Partnership [Member]	'	'
OPERATING ACTIVITIES	'	'
Net income	139,664	147,847
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation and amortization	176,207	137,302
Amortization of deferred financing costs	3,727	2,952
Equity in earnings of unconsolidated joint ventures	-7,297	-3,973
Distributions from unconsolidated joint ventures	0	613
Gain on property dispositions	-48,170	-49,367
Share-based compensation	10,422	8,174
Other	-5,202	-6,248
Changes in operating assets and liabilities:	'	'
Restricted cash	28,469	-2,703
Accounts receivable	-4,771	231
Deferred rent receivable	-11,928	-6,171
Prepaid expenses and other assets	-38,882	-50,389
Accounts payable	18,824	15,494
Accrued interest	15,500	18,922
Other liabilities	-26,232	2,352
Net cash provided by operating activities	250,331	215,036
INVESTING ACTIVITIES	'	'
Investment in operating properties - acquisitions	-97,677	-161,404
Investment in operating properties - other	-61,480	-40,433
Investments in and advances to unconsolidated joint ventures	-13,894	-11,736
Distributions from unconsolidated joint ventures	10,213	6,825
Net proceeds from disposition of properties/land	351,301	134,024
Net proceeds from public reimbursement receivable/escrow	5,501	12,943
Investment in development in progress	-222,484	-81,736
Investment in land held for development	-73,547	-34,642
Investment in deferred leasing costs	-28,409	-22,996
Net cash used in investing activities	-130,476	-199,155
FINANCING ACTIVITIES	'	'
Redemption of preferred units	0	-64,500
Proceeds from unsecured notes	0	448,646
Redemption of unsecured notes	-200,000	0
Proceeds from mortgage loans	0	10,401
Repayments of mortgage loans	-9,329	-3,977
Proceeds from credit facility	179,750	344,050
Repayments on credit facility	-38,800	-436,050
Payment of deferred financing costs	-3,622	-3,883
Capital contributions	44,097	954,481
Distributions to partners	-215,471	-178,589
Net cash (used in) provided by financing activities	-243,375	1,070,579
Net (decrease) increase in cash and cash equivalents	-123,520	1,086,460
Decrease in cash and cash equivalents related to foreign currency translation	-808	-246
Cash and cash equivalents at beginning of period	163,414	38,356
Cash and cash equivalents at end of period	$39,086	$1,124,570

Organization_and_Basis_of_Pres

Organization and Basis of Presentation	9 Months Ended
	Sep. 30, 2014
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, 2014. The Company provides leasing, property management, development, acquisition, and other tenant-related services. The Company owns and operates industrial properties nationally and owns and operates office properties primarily in Metro Philadelphia, Washington D.C. and certain sunbelt cities. 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.
	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, 2013. 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. Certain amounts from prior periods have been reclassified to conform to the current period presentation including reclassifying the accompanying statements of comprehensive income for discontinued operations.
	Recently Issued Accounting Standards
	In April 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update (ASU) 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360), Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity ("ASU 2014-08"), which changes the requirements for reporting discontinued operations. Under ASU 2014-08, a disposal of a component of an entity or a group of components of an entity is required to be reported in discontinued operations if the disposal represents a strategic shift that has (or will have) a major effect on an entity's operations and financial results when the component or group of components meets the criteria to be classified as held for sale or when the component or group of components is disposed of by sale or other than by sale. Generally, the sale of a real estate asset would not meet the discontinued operations criteria and would not be presented as such under ASU 2014-08. ASU 2014-08 also requires additional disclosures about both discontinued operations and the disposal of an individually significant component of an entity that does not qualify for discontinued operations presentation in the financial statements. The Company has adopted the provisions of ASU 2014-08 effective January 1, 2014, and has applied the provisions prospectively.
	In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09"), which supersedes nearly all existing revenue recognition guidance. The standard clarifies the required factors that an entity must consider when recognizing revenue. The standard also requires additional disclosures concerning contracts with customers, judgments concerning revenue recognition, and assets recognized for the costs to obtain or fulfill a contract. ASU 2014-09 is effective for the Company beginning January 1, 2017. The Company is evaluating the impact ASU 2014-09 will have on its financial position and results of operations.

Income_per_Common_Share_of_the

Income per Common Share of the Trust	9 Months Ended
	Sep. 30, 2014
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, 2014					September 30, 2013
		Income		Weighted	Per Share		Income		Weighted	Per Share
		(Loss) (Numerator)		Average			(Numerator)		Average
				Shares					Shares
				(Denominator)					(Denominator)
	Basic income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	34,290	147,422	$	0.23	$	22,316	135,628	$	0.16
	Dilutive shares for long-term compensation plans	—		666			—		700
	Diluted income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	34,290	148,088	$	0.23	$	22,316	136,328	$	0.16
	Basic income from discontinued operations
	Discontinued operations net of noncontrolling interest	$	133	147,422	$	—	$	6,383	135,628	$	0.05
	Dilutive shares for long-term compensation plans	—		666			—		700
	Diluted income from discontinued operations
	Discontinued operations net of noncontrolling interest	$	133	148,088	$	—	$	6,383	136,328	$	0.05
	Basic income per common share
	Net income available to common shareholders	$	34,423	147,422	$	0.23	$	28,699	135,628	$	0.21
	Dilutive shares for long-term compensation plans	—		666			—		700
	Diluted income per common share
	Net income available to common shareholders	$	34,423	148,088	$	0.23	$	28,699	136,328	$	0.21
		For the Nine Months Ended					For the Nine Months Ended
		September 30, 2014					September 30, 2013
		Income		Weighted	Per Share		Income		Weighted	Per Share
		(Numerator)		Average			(Numerator)		Average
				Shares					Shares
				(Denominator)					(Denominator)
	Basic income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	88,430	146,987	$	0.6	$	72,048	124,889	$	0.58
	Dilutive shares for long-term compensation plans	—		674			—		766
	Diluted income from continuing operations
	Income from continuing operations net of noncontrolling interest	88,430		147,661	$	0.6	72,048		125,655	$	0.57
	Basic income from discontinued operations
	Discontinued operations net of noncontrolling interest	47,142		146,987	$	0.32	67,999		124,889	$	0.54
	Dilutive shares for long-term compensation plans	—		674			—		766
	Diluted income from discontinued operations
	Discontinued operations net of noncontrolling interest	47,142		147,661	$	0.32	67,999		125,655	$	0.54
	Basic income per common share
	Net income available to common shareholders	135,572		146,987	$	0.92	140,047		124,889	$	1.12
	Dilutive shares for long-term compensation plans	—		674			—		766
	Diluted income per common share
	Net income available to common shareholders	$	135,572	147,661	$	0.92	$	140,047	125,655	$	1.11
	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. The amount of anti-dilutive options excluded from the computation of diluted income per common share for the three and nine months ended September 30, 2014 were 1,183,000 and 850,000, respectively, as compared to 994,000 and 959,000, respectively, for the same periods in 2013.
Stock Option Exercises [Text Block]	'
	During the three months ended September 30, 2014, no common shares were issued upon the exercise of options. During the nine months ended September 30, 2014, 43,000 common shares were issued upon the exercise of options. During the year ended December 31, 2013, 504,000 common shares were issued upon the exercise of options.

Income_per_Common_Unit_of_the_

Income per Common Unit of the Operating Partnership	9 Months Ended
	Sep. 30, 2014
Earnings Per Share, 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, 2014						September 30, 2013
		Income			Weighted	Per Share		Income			Weighted	Per Share
		(Loss) (Numerator)			Average			(Numerator)			Average
					Shares						Shares
					(Denominator)						(Denominator)
	Basic income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	34,290		147,422	$	0.23	$	22,316		135,628	$	0.16
	Dilutive shares for long-term compensation plans	—			666			—			700
	Diluted income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	34,290		148,088	$	0.23	$	22,316		136,328	$	0.16
	Basic income from discontinued operations
	Discontinued operations net of noncontrolling interest	$	133		147,422	$	—	$	6,383		135,628	$	0.05
	Dilutive shares for long-term compensation plans	—			666			—			700
	Diluted income from discontinued operations
	Discontinued operations net of noncontrolling interest	$	133		148,088	$	—	$	6,383		136,328	$	0.05
	Basic income per common share
	Net income available to common shareholders	$	34,423		147,422	$	0.23	$	28,699		135,628	$	0.21
	Dilutive shares for long-term compensation plans	—			666			—			700
	Diluted income per common share
	Net income available to common shareholders	$	34,423		148,088	$	0.23	$	28,699		136,328	$	0.21
		For the Nine Months Ended						For the Nine Months Ended
		September 30, 2014						September 30, 2013
		Income			Weighted	Per Share		Income			Weighted	Per Share
		(Numerator)			Average			(Numerator)			Average
					Shares						Shares
					(Denominator)						(Denominator)
	Basic income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	88,430		146,987	$	0.6	$	72,048		124,889	$	0.58
	Dilutive shares for long-term compensation plans	—			674			—			766
	Diluted income from continuing operations
	Income from continuing operations net of noncontrolling interest	88,430			147,661	$	0.6	72,048			125,655	$	0.57
	Basic income from discontinued operations
	Discontinued operations net of noncontrolling interest	47,142			146,987	$	0.32	67,999			124,889	$	0.54
	Dilutive shares for long-term compensation plans	—			674			—			766
	Diluted income from discontinued operations
	Discontinued operations net of noncontrolling interest	47,142			147,661	$	0.32	67,999			125,655	$	0.54
	Basic income per common share
	Net income available to common shareholders	135,572			146,987	$	0.92	140,047			124,889	$	1.12
	Dilutive shares for long-term compensation plans	—			674			—			766
	Diluted income per common share
	Net income available to common shareholders	$	135,572		147,661	$	0.92	$	140,047		125,655	$	1.11
	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. The amount of anti-dilutive options excluded from the computation of diluted income per common share for the three and nine months ended September 30, 2014 were 1,183,000 and 850,000, respectively, as compared to 994,000 and 959,000, respectively, for the same periods in 2013.
Stock Option Exercises [Text Block]	'
	During the three months ended September 30, 2014, no common shares were issued upon the exercise of options. During the nine months ended September 30, 2014, 43,000 common shares were issued upon the exercise of options. During the year ended December 31, 2013, 504,000 common shares were issued upon the exercise of options.
Liberty Property Limited Partnership [Member]	'
Earnings Per Share, 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, 2014						September 30, 2013
		Income			Weighted	Per Unit		Income			Weighted	Per Unit
		(Loss) (Numerator)			Average Units			(Numerator)			Average Units
					(Denominator)						(Denominator)
	Income from continuing operations - net of noncontrolling interest - consolidated joint ventures	$	35,231					$	22,998
	Less: Preferred unit distributions	(118		)				(118		)
	Basic income from continuing operations
	Income from continuing operations available to common unitholders	$	35,113		150,976	$	0.23	$	22,880		139,320	$	0.16
	Dilutive units for long-term compensation plans	—			666			—			700
	Diluted income from continuing operations
	Income from continuing operations available to common unitholders	$	35,113		151,642	$	0.23	$	22,880		140,020	$	0.16
	Basic income from discontinued operations
	Discontinued operations	$	136		150,976	$	—	$	6,544		139,320	$	0.05
	Dilutive units for long-term compensation plans	—			666			—			700
	Diluted income from discontinued operations
	Discontinued operations	$	136		151,642	$	—	$	6,544		140,020	$	0.05
	Basic income per common unit
	Income available to common unitholders	$	35,249		150,976	$	0.23	$	29,424		139,320	$	0.21
	Dilutive units for long-term compensation plans	—			666			—			700
	Diluted income per common unit
	Income available to common unitholders	$	35,249		151,642	$	0.23	$	29,424		140,020	$	0.21
		For the Nine Months Ended						For the Nine Months Ended
		September 30, 2014						September 30, 2013
		Income			Weighted	Per Unit		Income			Weighted	Per Unit
		(Numerator)			Average Units			(Numerator)			Average Units
					(Denominator)						(Denominator)
	Income from continuing operations net of noncontrolling interest - consolidated joint ventures	$	90,914					$	77,433
	Less: Preferred unit distributions	(354		)				(2,001		)
	Excess of preferred unit redemption over carrying amount	—						(1,236		)
	Basic income from continuing operations
	Income from continuing operations available to common unitholders	90,560			150,541	$	0.6	74,196			128,595	$	0.58
	Dilutive units for long-term compensation plans	—			674			—			766
	Diluted income from continuing operations
	Income from continuing operations available to common unitholders	90,560			151,215	$	0.6	74,196			129,361	$	0.57
	Basic income from discontinued operations
	Discontinued operations	48,276			150,541	$	0.32	70,008			128,595	$	0.54
	Dilutive units for long-term compensation plans	—			674			—			766
	Diluted income from discontinued operations
	Discontinued operations	48,276			151,215	$	0.32	70,008			129,361	$	0.54
	Basic income per common unit
	Income available to common unitholders	138,836			150,541	$	0.92	144,204			128,595	$	1.12
	Dilutive units for long-term compensation plans	—			674			—			766
	Diluted income per common unit
	Income available to common unitholders	$	138,836		151,215	$	0.92	$	144,204		129,361	$	1.11
	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. The amount of anti-dilutive options excluded from the computation of diluted income per common unit for the three and nine months ended September 30, 2014 were 1,183,000 and 850,000, respectively, as compared to 994,000 and 959,000, respectively, for the same periods in 2013.
Stock Option Exercises [Text Block]	'
	During the three months ended September 30, 2014, no common units were issued upon exercise of options. During the nine months ended September 30, 2014, 43,000 common units were issued upon the exercise of options. During the year ended December 31, 2013, 504,000 common units were issued upon the exercise of options.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Accumulated Other Comprehensive Income (Loss) Note [Text Block]	'
	Accumulated Other Comprehensive Income
	The following table sets forth the components of Accumulated Other Comprehensive Income (in thousands):
		Nine Months Ended September 30,
		2014			2013
	Foreign Currency Translation:
	Beginning balance	$	8,592		$	3,195
	Translation adjustment	(5,189		)	115
	Ending balance	3,403			3,310
	Net unrealized gain on derivative instruments:
	Beginning balance	1,584			—
	Unrealized losses	(990		)	—
	Ending balance	594			—
	Total accumulated other comprehensive income	3,997			3,310
	Less: portion included in noncontrolling interest – operating partnership	(290		)	(272		)
	Total accumulated other comprehensive income included in shareholders' equity	$	3,707		$	3,038

Segment_Information

Segment Information	9 Months Ended
	Sep. 30, 2014
Segment Reporting, Measurement Disclosures [Abstract]	'
Segment Information	'
	Segment Information
	The Company owns and operates industrial properties nationally and owns and operates office properties primarily in Metro Philadelphia, Washington D.C. and certain sunbelt cities. Additionally, the Company owns certain assets in the United Kingdom. The Company's reportable segments are as follows.
	•	Carolinas;
	•	Chicago/Milwaukee;
	•	Houston;
	•	Lehigh/Central PA;
	•	Minnesota;
	•	Orlando;
	•	Philadelphia;
	•	Richmond/Hampton Roads;
	•	Southeastern PA;
	•	South Florida;
	•	Tampa;
	•	United Kingdom.
	Certain other segments are aggregated into an "Other" category which includes the reportable segments: Arizona; Atlanta; Cincinnati/Columbus/Indianapolis; Dallas; Jacksonville; Maryland; New Jersey; Northern Virginia; Southern California; Washington D.C. and other.
	The Company evaluates the performance of its reportable segments based on net operating income. Net operating income includes operating revenue from external customers, real estate taxes, 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):
				For the Three Months							For the Nine Months
				Ended September 30							Ended September 30
				2014				2013			2014			2013
	Operating revenue
		Carolinas		$	9,479			$	7,626		$	26,282		$	22,213
		Chicago/Milwaukee		8,004				3,067			24,727			9,230
		Houston		12,833				9,481			36,828			26,833
		Lehigh/Central PA		30,034				24,981			87,853			74,339
		Minnesota		13,925				15,591			41,217			46,319
		Orlando		8,463				7,583			24,519			23,156
		Philadelphia		8,303				7,633			26,402			23,027
		Richmond/Hampton Roads		10,358				9,959			30,542			29,899
		South Florida		12,012				8,798			36,028			26,032
		Southeastern PA		36,087				41,251			110,833			122,694
		Tampa		13,597				12,767			40,001			38,849
		United Kingdom		4,111				1,400			12,430			3,620
		Other		31,144				33,100			96,300			93,546
	Segment-level operating revenue			198,350				183,237			593,962			539,757
	Reconciliation to total operating revenues
		Discontinued operations		(9		)		(28,007		)	(4,728		)	(86,604		)
		Other		15				118			(288		)	345
	Total operating revenue			$	198,356			$	155,348		$	588,946		$	453,498
	Net operating income
		Carolinas		$	6,570			$	5,182		$	18,006		$	15,035
		Chicago/Milwaukee		5,382				2,163			15,518			6,149
		Houston		7,510				5,426			21,794			15,735
		Lehigh/Central PA		21,634				17,204			60,647			50,422
		Minnesota		6,575				7,289			19,964			22,563
		Orlando		5,411				5,128			16,257			15,504
		Philadelphia		6,736				5,919			20,247			16,869
		Richmond/Hampton Roads		6,144				5,899			18,118			17,978
		South Florida		6,647				4,735			21,066			14,168
		Southeastern PA		20,516				23,754			60,175			68,622
		Tampa		8,213				7,916			25,142			24,522
		United Kingdom		2,468				123			8,716			(331		)
		Other		20,715				18,555			61,614			51,346
	Segment-level net operating income			124,521				109,293			367,264			318,582
	Reconciliation to income from continuing operations
		Interest expense (1)		(37,958		)		(37,412		)	(116,192		)	(101,632		)
		Depreciation/amortization expense (1) (2)		(44,538		)		(29,963		)	(133,636		)	(88,330		)
		(Loss) gain on property dispositions		(20		)		—			1,879			—
		Equity in earnings of unconsolidated joint ventures		1,592				650			7,297			3,973
		General and administrative expense (1) (2)		(8,556		)		(12,394		)	(29,189		)	(35,215		)
		Discontinued operations excluding gain on property dispositions		(98		)		(6,515		)	(1,985		)	(20,641		)
		Income taxes (2)		(821		)		(636		)	(1,966		)	(1,772		)
	Other		1,193				381			(2,084		)	2,874
Income from continuing operations			$	35,315			$	23,404		$	91,388		$	77,839
-1	Includes activity on discontinued operations.
-2	Excludes costs which are included in determining segment-level net operating income.
The Company's total assets by reportable segment as of September 30, 2014 and December 31, 2013 are as follows (in thousands):
		September 30,				December 31,
		2014				2013
Total assets
	Carolinas	$	319,083			$	257,230
	Chicago/Milwaukee	417,134				413,585
	Houston	434,835				380,248
	Lehigh/Central PA	993,699				938,824
	Minnesota	352,447				335,613
	Orlando	255,961				253,888
	Philadelphia	350,342				316,810
	Richmond/Hampton Roads	248,186				250,008
	South Florida	393,910				380,138
	Southeastern PA	711,190				695,966
	Tampa	335,229				337,300
	United Kingdom	241,362				247,537
	Other	1,528,019				1,735,393
Segment-level total assets		6,581,397				6,542,540
	Corporate Other	79,445				233,020
Total assets		$	6,660,842			$	6,775,560
During the three months ended September 30, 2014, the Company acquired one property for a purchase price of $6.8 million. During the nine months ended September 30, 2014, the Company acquired nine properties for a total purchase price of $97.7 million.
The Company did not sell any operating properties during the three months ended September 30, 2014. During the nine months ended September 30, 2014, the Company realized proceeds of $366.9 million from the sale of 52 properties and 19 acres of land. Included in these properties were three operating properties sold for $32.2 million to a joint venture in which the Company retains a 25% interest.

Accounting_for_the_Impairment_

Accounting for the Impairment or Disposal of Long-Lived Assets	9 Months Ended
	Sep. 30, 2014
Disposal Group, Including Discontinued Operation, Long Lived Assets [Abstract]	'
Disposal Groups, Including Discontinued Operations, Disclosure [Text Block]	'
	Accounting for the Disposal of Long-Lived Assets
	Under ASU 2014-08, a disposal of a component of an entity is required to be reported in discontinued operations if the disposal represents a strategic shift that has (or will have) a major effect on an entity's operations and financial results.
	In November 2013, the Company entered into an Agreement of Sale and Purchase pursuant to which the Company agreed to sell 97 operating properties containing an aggregate of 6.6 million square feet for $697.3 million (the "Portfolio Sale"). In December 2013, the Company closed on the first of two planned settlements under this agreement. The proceeds from the first settlement were $367.7 million and included 49 properties totaling approximately 4.0 million square feet of space and 140 acres of land. In January 2014, the Company closed on the remaining settlement for proceeds of $329.6 million which consisted of 23 properties totaling 1.4 million square feet and 19 acres of land in the Maryland reportable segment, 24 properties and 1.2 million square feet in the New Jersey reportable segment and one property totaling 37,000 square feet in the Company's Southeastern PA reportable segment.
	The Portfolio Sale is considered a discontinued operation under the provisions of ASU 2014-08 as it represents a strategic shift that will have a major effect on the Company's operations and financial results.
	Prior to the adoption of ASU 2014-08, the results of operations for all operating properties sold or held for sale during the reported periods were shown under discontinued operations on the consolidated statements of comprehensive income. Under ASU 2014-08, operating properties that were sold or classified as held for sale before the adoption of ASU 2014-08 continue to be classified as discontinued operations. Accordingly, operating properties previously reported as discontinued operations will continue to be presented as discontinued operations on the consolidated statements of comprehensive income for all periods presented. The proceeds from the disposition of properties excluding the Portfolio Sale that were included in discontinued operations were $126.0 million for the nine months ended September 30, 2013.
	A summary of the results of operations for the Portfolio Sale and other properties classified as discontinued operations through the respective disposition dates is as follows (in thousands):
			For the Three Months Ended						For the Nine Months Ended
			September 30, 2014			September 30, 2013			September 30, 2014			September 30, 2013
	Portfolio Sale
		Revenues	$	9		$	27,585		$	4,728		$	81,385
		Operating expenses	86			(10,606		)	(2,233		)	(29,155		)
		Interest and other income	3			66			40			172
		Interest expense	—			(3,830		)	(557		)	(11,550		)
		Depreciation and amortization	—			(6,798		)	—			(21,403		)
		Income before (loss) gain on property dispositions	98			6,417			1,978			19,449
		(Loss) gain on property dispositions	(35		)	—			46,086			—
		Income from discontinued operations - Portfolio Sale	63			6,417			48,064			19,449
		Noncontrolling interest	(1		)	(158		)	(1,130		)	(558		)
		Income from discontinued operations available to common shareholders - Portfolio Sale	62			6,259			46,934			18,891
		Add back noncontrolling interest	1			158			1,130			558
		Income from discontinued operations - Portfolio Sale	63			6,417			48,064			19,449
		Income from discontinued operations - other properties	73			127			212			50,559
		Income from discontinued operations	$	136		$	6,544		$	48,276		$	70,008
	Net cash used in operating activities from the properties included in the Portfolio Sale for the three and nine months ended September 30, 2014 was $1.5 million and $4.3 million, respectively, compared to net cash provided by operating activities from such properties of $11.5 million and $39.5 million, respectively, for the three and nine months ended September 30, 2013. Net cash used in investing activities from the properties included in the Portfolio Sale for the three months ended September 30, 2014 was $42,000 and net cash provided by investing activities was $313.1 million for the nine months ended September 30, 2014. Net cash used by investing activities from such properties was $3.4 million and $11.1 million, respectively, for the three and nine months ended September 30, 2013.
	Interest expense has been allocated to discontinued operations. The allocation of interest expense to discontinued operations was based on the ratio of net assets sold and held for sale (without continuing involvement) to the sum of total net assets plus consolidated debt.
	During the three months ended September 30, 2014, the Company did not sell any operating properties. During the nine months ended September 30, 2014, the Company sold four operating properties in segments grouped into the Company's "Other" category for aggregate proceeds of $37.3 million. One property totaling 75,000 square feet in the Company’s "Other" category was considered held for sale as of September 30, 2014. Under ASU 2014-08, these sold and held for sale properties have not been classified as discontinued operations.

Noncontrolling_Interests_of_th

Noncontrolling Interests of the Trust	9 Months Ended
	Sep. 30, 2014
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 outstanding of the Operating Partnership not held by the Trust as of September 30, 2014 have the same economic characteristics as common shares of the Trust. The 3,553,566 outstanding common units of the Operating Partnership at such date 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 3,553,566 outstanding common units based on the closing price of the common shares of the Trust at September 30, 2014 was $118.2 million.

Limited_Partners_Equity_of_the

Limited Partners' Equity of the Operating Partnership	9 Months Ended
	Sep. 30, 2014
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 outstanding of the Operating Partnership not held by the Trust as of September 30, 2014 have the same economic characteristics as common shares of the Trust. The 3,553,566 outstanding common units of the Operating Partnership at such date 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 3,553,566 outstanding common units based on the closing price of the common shares of the Trust at September 30, 2014 was $118.2 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 as of September 30, 2014 have the same economic characteristics as common shares of the Trust. The 3,553,566 outstanding common units at such date are the limited partners' equity - common units held by persons and entities other than the Trust, the general partner of the Operating Partnership, which holds a number of common units equal to the number of outstanding common shares of beneficial interest. The common units share proportionately in the net income or loss and in any distributions of the Operating Partnership and are exchangeable into the same number of common shares of the Trust. The market value of the 3,553,566 outstanding common units at September 30, 2014 based on the closing price of the common shares of the Trust at September 30, 2014 was $118.2 million.

Noncontrolling_Interest_Operat

Noncontrolling Interest - Operating Partnership/Limited Partners' Equity - Preferred Units	9 Months Ended
	Sep. 30, 2014
Temporary Equity [Line Items]	'
Stockholders' Equity Note Disclosure [Text Block]	'
	Noncontrolling Interest - Operating Partnership/Limited Partners' Equity - Preferred Units
	As of September 30, 2014, the following cumulative preferred units of the Operating Partnership were outstanding:
	ISSUE	AMOUNT		UNITS	LIQUIDATION	DIVIDEND
					PREFERENCE	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.

Indebtedness

Indebtedness	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Debt Disclosure [Text Block]	'
	Indebtedness
	Credit Facility
	In March 2014, the Company replaced its existing $500 million credit facility which was due in November 2015 with a new credit facility. The new facility (the "Credit Facility") is for $800 million. It matures in March 2018 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 new facility bear interest at LIBOR plus 105 basis points. There is also a 20 basis point annual facility fee on the current borrowing capacity. The 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 facility.
	The Credit Facility contains financial covenants, certain of which are set forth below:
	•	total debt to total assets may not exceed 0.60:1;
	•	earnings before interest, taxes, depreciation and amortization to fixed charges may not be less than 1.50:1;
	•	unsecured debt to unencumbered asset value must equal or be less than 60%; and
	•	unencumbered net operating income to unsecured interest expense must equal or exceed 175%.
	As of September 30, 2014, the Company was in compliance with the Credit Facility financial covenants.
	Unsecured Notes
	In August 2014, the Company repaid its 5.65% Senior Notes which were due in August 2014 in the amount of $200 million.

Disclosure_of_Fair_Value_of_Fi

Disclosure of Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2014
Debt Instrument, Fair Value Disclosure [Abstract]	'
Disclosure of Fair Value of Financial Instruments	'
	Disclosure of Fair Value of Financial Instruments
	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, 2014 and December 31, 2013. 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 used a discounted cash flow model to determine the estimated fair value of its debt as of September 30, 2014.  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, 2013 and September 30, 2014 (in thousands):
		Mortgage Loans				Unsecured Notes
		Carrying Value		Fair Value		Carrying Value		Fair Value
	As of December 31, 2013	$	545,306	$	573,944	$	2,708,213	$	2,764,831
	As of September 30, 2014	$	534,547	$	550,722	$	2,508,886	$	2,634,931

Investment_in_Unconsolidated_J

Investment in Unconsolidated Joint Ventures	9 Months Ended
	Sep. 30, 2014
Equity Method Investments and Joint Ventures [Abstract]	'
Equity Method Investments and Joint Ventures Disclosure [Text Block]	'
	Investment in Unconsolidated Joint Ventures
	Comcast Innovation & Technology Center
	On June 30, 2014, the Company entered into two joint ventures for the purpose of developing and owning the Comcast Innovation & Technology Center (the "Project") located on the 1800 block of Arch Street in Philadelphia, Pennsylvania as part of a trophy-class mixed-use development. The 59-story building will include 1.3 million square feet of rentable office space (the "Office") and a 220-room Four Seasons Hotel (the "Hotel").  Completion of the first phase of the Project is anticipated to be in the third quarter of 2017. Project costs for the development of the Project, exclusive of tenant-funded interior improvements, are anticipated to be approximately $921 million.  The Company's investment in the project is expected to be approximately $184 million with 20% ownership interests in both joint ventures. As of September 30, 2014, the Company's investment in these joint ventures was $17.4 million and is reflected in investments in and advances to unconsolidated joint ventures in the Company's consolidated balance sheet. During the three months ended September 30, 2014, the Company began development on the building and as of September 30, 2014, the total development in progress for the Project was $85.5 million.
	The two joint ventures have engaged the Company as the developer of the Project pursuant to a Development Agreement by which the Company agrees, in consideration for a development fee, to be responsible for all aspects of the development of the Project and to guarantee the timely lien-free completion of construction of the Project and the payment, subject to certain exceptions, of any cost overruns incurred in the development of the Project. During the three and nine months ended September 30, 2014, the Company recognized $0.7 million in developer fees related to the project. These fees are included in other income in the Company's consolidated statement of comprehensive income.
	Comcast Corporation has signed a 20-year lease for 982,275 square feet, or approximately 73.4% of the office space in the Office.  The Company will manage and lease the Office and Four Seasons Hotels Limited will manage the Hotel.
	Liberty Venture I, LP
	During the nine months ended September 30, 2014, Liberty Venture I, LP, an unconsolidated joint venture in which the Company holds a 25% interest, acquired three properties comprising 603,000 square feet from the Company for $32.2 million.

Business_Combination

Business Combination	9 Months Ended
	Sep. 30, 2014
Business Combinations [Abstract]	'
Business Combination Disclosure [Text Block]	'
	Business Combination
	On October 8, 2013, the Company acquired all of the outstanding general and limited partnership interests of Cabot Industrial Fund III Operating Partnership, L.P., a Delaware limited partnership (the "Cabot Acquisition"). The acquisition resulted in the purchase of a 100% ownership interest in 177 industrial assets totaling approximately 23.0 million square feet. The purchase price for the Cabot Acquisition was $1.469 billion, which was paid through the assumption of approximately $229.8 million of mortgage debt and the remainder in cash. The Company funded the cash portion of the acquisition consideration through a combination of proceeds from an August 2013 equity offering, proceeds from a September 2013 offering of senior notes and draws under its Credit Facility.
	The allocation of purchase price of the Cabot Acquisition is preliminary pending the receipt of the information necessary to complete the resolution of certain tangible and intangible assets and liabilities including the reconciliation of working capital accounts and the completion of tenant operating expense reconciliations.

Derivative_Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'
Interest rate swaps [Text Block]	'
	Derivative Instruments
	We borrow funds at a combination of fixed and variable rates. Borrowings under our revolving credit facility and certain bank mortgage loans bear interest at variable rates. Our long-term debt typically bears interest at fixed rates. Our interest rate risk management objectives are to limit generally the impact of interest rate changes on earnings and cash flows and to lower our overall borrowing costs. To achieve these objectives, from time to time, we enter 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. We generally do not hold or issue these derivative contracts for trading or speculative purposes. The interest rate on all of our variable rate debt is generally adjusted at one or three month intervals, subject to settlements under interest rate hedge contracts.
	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 income (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.
	In connection with the Cabot Acquisition, the Company assumed the seller’s 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 that were also assumed. The Swaps had aggregate notional amounts of $104.1 million and $105.2 million at September 30, 2014 and December 31, 2013, respectively, and expire at various dates between 2018 and 2020.
	For the three months ended September 30, 2014, the effective portion of the change in the fair value of the swaps was an increase in the amount of $666,000 which was recorded as an increase in other comprehensive income. For the nine months ended September 30, 2014, the effective portion of the change in the fair value of the swaps was a decrease in the amount of $990,000, which was recorded as a reduction of other comprehensive income. These amounts reported in accumulated other comprehensive income will be reclassified to interest expense as interest payments are made on the variable rate mortgages. The amount of loss reclassified from accumulated other comprehensive income was $367,000 and $1.1 million for the three and nine months ended September 30, 2014, respectively. The ineffective portion of the change in the fair value of the Swaps for the three months ended September 30, 2014 in the amount of $13,000 was recorded as a decrease to interest expense in the accompanying consolidated statements of comprehensive income. The ineffective portion of the change in the fair value of the Swaps for the nine months ended September 30, 2014 in the amount of $42,000 was recorded as an increase to interest expense in the accompanying consolidated statements of comprehensive income.
	The fair value of the Swaps in the amount of $8.0 million and $8.4 million as of September 30, 2014 and December 31, 2013, respectively, is included in other liabilities in the accompanying consolidated balance sheets. The Company estimates that $1.3 million will be reclassified from accumulated other comprehensive income 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 default 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 for approximately $8.3 million.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2014
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, 2014, were as follows (in thousands):
	Year	Amount
	2014	$	102
	2015	428
	2016	447
	2017	447
	2018	447
	2019 through 2034	6,173
	Total	$	8,044
	Operating ground lease expense for the three and nine months ended September 30, 2014 were $114,000 and $289,000, respectively, as compared to $42,000 and $125,000, respectively, for the same periods in 2013.
	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, 2014 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, 2014, the Company had letter of credit obligations of $8.9 million. The Company believes that the likelihood is remote that there will be a draw upon these letter of credit obligations.
	As of September 30, 2014, the Company had 22 buildings under development. These buildings are expected to contain, when completed, a total of 4.7 million square feet of leasable space and represent an anticipated aggregate investment of $428.7 million. At September 30, 2014, development in progress totaled $250.5 million. In addition, as of September 30, 2014, the Company had invested $6.6 million in deferred leasing costs related to these development buildings. See Note 12 for details of the Company's commitments related to the development of the Comcast Innovation and Technology Center. In addition, the Company had a signed commitment for a build-to-suit development not yet commenced for an anticipated investment of $20.4 million.
	As of September 30, 2014, the Company was committed to $12.8 million in improvements on certain buildings and land parcels.
	As of September 30, 2014, the Company was committed to $56.3 million in future land purchases.
	As of September 30, 2014, the Company was obligated to pay for tenant improvements not yet completed for a maximum of $52.1 million.
	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_Sta

Supplemental Disclosure to Statements of Cash Flows	9 Months Ended
	Sep. 30, 2014
Supplemental Cash Flow Information [Abstract]	'
Supplemental Disclosure to Statements of Cash Flows	'
	Supplemental Disclosure to Statements of Cash Flows
	The following are supplemental disclosures to the statements of cash flows for the nine months ended September 30, 2014 and 2013 (amounts in thousands):
		2014			2013
	Write-off of fully depreciated property and deferred costs	$	31,322		$	23,180
	Write-off of depreciated property and deferred costs due to sale	$	132,707		$	49,618
	Unrealized losses on cash flow hedge	$	(990	)	$	—
	Write-off of origination costs relating to preferred unit redemptions	$	—		$	1,236
	Increase in investments in and advances to unconsolidated joint ventures due to disposition activity	$	(11,948	)	$	—
	Changes in accrued development capital expenditures	$	7,854		$	12,869
	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.

Organization_and_Basis_of_Pres1

Organization and Basis of Presentation (Policy)	9 Months Ended
	Sep. 30, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
New Accounting Pronouncements, Policy [Policy Text Block]	'
	Recently Issued Accounting Standards
	In April 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update (ASU) 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360), Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity ("ASU 2014-08"), which changes the requirements for reporting discontinued operations. Under ASU 2014-08, a disposal of a component of an entity or a group of components of an entity is required to be reported in discontinued operations if the disposal represents a strategic shift that has (or will have) a major effect on an entity's operations and financial results when the component or group of components meets the criteria to be classified as held for sale or when the component or group of components is disposed of by sale or other than by sale. Generally, the sale of a real estate asset would not meet the discontinued operations criteria and would not be presented as such under ASU 2014-08. ASU 2014-08 also requires additional disclosures about both discontinued operations and the disposal of an individually significant component of an entity that does not qualify for discontinued operations presentation in the financial statements. The Company has adopted the provisions of ASU 2014-08 effective January 1, 2014, and has applied the provisions prospectively.
	In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09"), which supersedes nearly all existing revenue recognition guidance. The standard clarifies the required factors that an entity must consider when recognizing revenue. The standard also requires additional disclosures concerning contracts with customers, judgments concerning revenue recognition, and assets recognized for the costs to obtain or fulfill a contract. ASU 2014-09 is effective for the Company beginning January 1, 2017. The Company is evaluating the impact ASU 2014-09 will have on its financial position and results of operations.

Income_per_Common_Share_of_the1

Income per Common Share of the Trust (Tables)	9 Months Ended
	Sep. 30, 2014
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, 2014					September 30, 2013
		Income		Weighted	Per Share		Income		Weighted	Per Share
		(Loss) (Numerator)		Average			(Numerator)		Average
				Shares					Shares
				(Denominator)					(Denominator)
	Basic income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	34,290	147,422	$	0.23	$	22,316	135,628	$	0.16
	Dilutive shares for long-term compensation plans	—		666			—		700
	Diluted income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	34,290	148,088	$	0.23	$	22,316	136,328	$	0.16
	Basic income from discontinued operations
	Discontinued operations net of noncontrolling interest	$	133	147,422	$	—	$	6,383	135,628	$	0.05
	Dilutive shares for long-term compensation plans	—		666			—		700
	Diluted income from discontinued operations
	Discontinued operations net of noncontrolling interest	$	133	148,088	$	—	$	6,383	136,328	$	0.05
	Basic income per common share
	Net income available to common shareholders	$	34,423	147,422	$	0.23	$	28,699	135,628	$	0.21
	Dilutive shares for long-term compensation plans	—		666			—		700
	Diluted income per common share
	Net income available to common shareholders	$	34,423	148,088	$	0.23	$	28,699	136,328	$	0.21
		For the Nine Months Ended					For the Nine Months Ended
		September 30, 2014					September 30, 2013
		Income		Weighted	Per Share		Income		Weighted	Per Share
		(Numerator)		Average			(Numerator)		Average
				Shares					Shares
				(Denominator)					(Denominator)
	Basic income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	88,430	146,987	$	0.6	$	72,048	124,889	$	0.58
	Dilutive shares for long-term compensation plans	—		674			—		766
	Diluted income from continuing operations
	Income from continuing operations net of noncontrolling interest	88,430		147,661	$	0.6	72,048		125,655	$	0.57
	Basic income from discontinued operations
	Discontinued operations net of noncontrolling interest	47,142		146,987	$	0.32	67,999		124,889	$	0.54
	Dilutive shares for long-term compensation plans	—		674			—		766
	Diluted income from discontinued operations
	Discontinued operations net of noncontrolling interest	47,142		147,661	$	0.32	67,999		125,655	$	0.54
	Basic income per common share
	Net income available to common shareholders	135,572		146,987	$	0.92	140,047		124,889	$	1.12
	Dilutive shares for long-term compensation plans	—		674			—		766
	Diluted income per common share
	Net income available to common shareholders	$	135,572	147,661	$	0.92	$	140,047	125,655	$	1.11

Income_per_Common_Unit_of_the_1

Income per Common Unit of the Operating Partnership (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share, 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, 2014						September 30, 2013
		Income			Weighted	Per Share		Income			Weighted	Per Share
		(Loss) (Numerator)			Average			(Numerator)			Average
					Shares						Shares
					(Denominator)						(Denominator)
	Basic income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	34,290		147,422	$	0.23	$	22,316		135,628	$	0.16
	Dilutive shares for long-term compensation plans	—			666			—			700
	Diluted income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	34,290		148,088	$	0.23	$	22,316		136,328	$	0.16
	Basic income from discontinued operations
	Discontinued operations net of noncontrolling interest	$	133		147,422	$	—	$	6,383		135,628	$	0.05
	Dilutive shares for long-term compensation plans	—			666			—			700
	Diluted income from discontinued operations
	Discontinued operations net of noncontrolling interest	$	133		148,088	$	—	$	6,383		136,328	$	0.05
	Basic income per common share
	Net income available to common shareholders	$	34,423		147,422	$	0.23	$	28,699		135,628	$	0.21
	Dilutive shares for long-term compensation plans	—			666			—			700
	Diluted income per common share
	Net income available to common shareholders	$	34,423		148,088	$	0.23	$	28,699		136,328	$	0.21
		For the Nine Months Ended						For the Nine Months Ended
		September 30, 2014						September 30, 2013
		Income			Weighted	Per Share		Income			Weighted	Per Share
		(Numerator)			Average			(Numerator)			Average
					Shares						Shares
					(Denominator)						(Denominator)
	Basic income from continuing operations
	Income from continuing operations net of noncontrolling interest	$	88,430		146,987	$	0.6	$	72,048		124,889	$	0.58
	Dilutive shares for long-term compensation plans	—			674			—			766
	Diluted income from continuing operations
	Income from continuing operations net of noncontrolling interest	88,430			147,661	$	0.6	72,048			125,655	$	0.57
	Basic income from discontinued operations
	Discontinued operations net of noncontrolling interest	47,142			146,987	$	0.32	67,999			124,889	$	0.54
	Dilutive shares for long-term compensation plans	—			674			—			766
	Diluted income from discontinued operations
	Discontinued operations net of noncontrolling interest	47,142			147,661	$	0.32	67,999			125,655	$	0.54
	Basic income per common share
	Net income available to common shareholders	135,572			146,987	$	0.92	140,047			124,889	$	1.12
	Dilutive shares for long-term compensation plans	—			674			—			766
	Diluted income per common share
	Net income available to common shareholders	$	135,572		147,661	$	0.92	$	140,047		125,655	$	1.11
Liberty Property Limited Partnership [Member]	'
Earnings Per Share, 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, 2014						September 30, 2013
		Income			Weighted	Per Unit		Income			Weighted	Per Unit
		(Loss) (Numerator)			Average Units			(Numerator)			Average Units
					(Denominator)						(Denominator)
	Income from continuing operations - net of noncontrolling interest - consolidated joint ventures	$	35,231					$	22,998
	Less: Preferred unit distributions	(118		)				(118		)
	Basic income from continuing operations
	Income from continuing operations available to common unitholders	$	35,113		150,976	$	0.23	$	22,880		139,320	$	0.16
	Dilutive units for long-term compensation plans	—			666			—			700
	Diluted income from continuing operations
	Income from continuing operations available to common unitholders	$	35,113		151,642	$	0.23	$	22,880		140,020	$	0.16
	Basic income from discontinued operations
	Discontinued operations	$	136		150,976	$	—	$	6,544		139,320	$	0.05
	Dilutive units for long-term compensation plans	—			666			—			700
	Diluted income from discontinued operations
	Discontinued operations	$	136		151,642	$	—	$	6,544		140,020	$	0.05
	Basic income per common unit
	Income available to common unitholders	$	35,249		150,976	$	0.23	$	29,424		139,320	$	0.21
	Dilutive units for long-term compensation plans	—			666			—			700
	Diluted income per common unit
	Income available to common unitholders	$	35,249		151,642	$	0.23	$	29,424		140,020	$	0.21
		For the Nine Months Ended						For the Nine Months Ended
		September 30, 2014						September 30, 2013
		Income			Weighted	Per Unit		Income			Weighted	Per Unit
		(Numerator)			Average Units			(Numerator)			Average Units
					(Denominator)						(Denominator)
	Income from continuing operations net of noncontrolling interest - consolidated joint ventures	$	90,914					$	77,433
	Less: Preferred unit distributions	(354		)				(2,001		)
	Excess of preferred unit redemption over carrying amount	—						(1,236		)
	Basic income from continuing operations
	Income from continuing operations available to common unitholders	90,560			150,541	$	0.6	74,196			128,595	$	0.58
	Dilutive units for long-term compensation plans	—			674			—			766
	Diluted income from continuing operations
	Income from continuing operations available to common unitholders	90,560			151,215	$	0.6	74,196			129,361	$	0.57
	Basic income from discontinued operations
	Discontinued operations	48,276			150,541	$	0.32	70,008			128,595	$	0.54
	Dilutive units for long-term compensation plans	—			674			—			766
	Diluted income from discontinued operations
	Discontinued operations	48,276			151,215	$	0.32	70,008			129,361	$	0.54
	Basic income per common unit
	Income available to common unitholders	138,836			150,541	$	0.92	144,204			128,595	$	1.12
	Dilutive units for long-term compensation plans	—			674			—			766
	Diluted income per common unit
	Income available to common unitholders	$	138,836		151,215	$	0.92	$	144,204		129,361	$	1.11

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2014
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 Income (in thousands):
		Nine Months Ended September 30,
		2014			2013
	Foreign Currency Translation:
	Beginning balance	$	8,592		$	3,195
	Translation adjustment	(5,189		)	115
	Ending balance	3,403			3,310
	Net unrealized gain on derivative instruments:
	Beginning balance	1,584			—
	Unrealized losses	(990		)	—
	Ending balance	594			—
	Total accumulated other comprehensive income	3,997			3,310
	Less: portion included in noncontrolling interest – operating partnership	(290		)	(272		)
	Total accumulated other comprehensive income included in shareholders' equity	$	3,707		$	3,038

Segment_Information_Tables

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2014
Segment Reporting, Measurement Disclosures [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):
				For the Three Months							For the Nine Months
				Ended September 30							Ended September 30
				2014				2013			2014			2013
	Operating revenue
		Carolinas		$	9,479			$	7,626		$	26,282		$	22,213
		Chicago/Milwaukee		8,004				3,067			24,727			9,230
		Houston		12,833				9,481			36,828			26,833
		Lehigh/Central PA		30,034				24,981			87,853			74,339
		Minnesota		13,925				15,591			41,217			46,319
		Orlando		8,463				7,583			24,519			23,156
		Philadelphia		8,303				7,633			26,402			23,027
		Richmond/Hampton Roads		10,358				9,959			30,542			29,899
		South Florida		12,012				8,798			36,028			26,032
		Southeastern PA		36,087				41,251			110,833			122,694
		Tampa		13,597				12,767			40,001			38,849
		United Kingdom		4,111				1,400			12,430			3,620
		Other		31,144				33,100			96,300			93,546
	Segment-level operating revenue			198,350				183,237			593,962			539,757
	Reconciliation to total operating revenues
		Discontinued operations		(9		)		(28,007		)	(4,728		)	(86,604		)
		Other		15				118			(288		)	345
	Total operating revenue			$	198,356			$	155,348		$	588,946		$	453,498
	Net operating income
		Carolinas		$	6,570			$	5,182		$	18,006		$	15,035
		Chicago/Milwaukee		5,382				2,163			15,518			6,149
		Houston		7,510				5,426			21,794			15,735
		Lehigh/Central PA		21,634				17,204			60,647			50,422
		Minnesota		6,575				7,289			19,964			22,563
		Orlando		5,411				5,128			16,257			15,504
		Philadelphia		6,736				5,919			20,247			16,869
		Richmond/Hampton Roads		6,144				5,899			18,118			17,978
		South Florida		6,647				4,735			21,066			14,168
		Southeastern PA		20,516				23,754			60,175			68,622
		Tampa		8,213				7,916			25,142			24,522
		United Kingdom		2,468				123			8,716			(331		)
		Other		20,715				18,555			61,614			51,346
	Segment-level net operating income			124,521				109,293			367,264			318,582
	Reconciliation to income from continuing operations
		Interest expense (1)		(37,958		)		(37,412		)	(116,192		)	(101,632		)
		Depreciation/amortization expense (1) (2)		(44,538		)		(29,963		)	(133,636		)	(88,330		)
		(Loss) gain on property dispositions		(20		)		—			1,879			—
		Equity in earnings of unconsolidated joint ventures		1,592				650			7,297			3,973
		General and administrative expense (1) (2)		(8,556		)		(12,394		)	(29,189		)	(35,215		)
		Discontinued operations excluding gain on property dispositions		(98		)		(6,515		)	(1,985		)	(20,641		)
		Income taxes (2)		(821		)		(636		)	(1,966		)	(1,772		)
		Other		1,193				381			(2,084		)	2,874
	Income from continuing operations			$	35,315			$	23,404		$	91,388		$	77,839
	-1	Includes activity on discontinued operations.
	-2	Excludes costs which are included in determining segment-level net operating income.
Reconciliation of Assets from Segment to Consolidated [Table Text Block]	'
	The Company's total assets by reportable segment as of September 30, 2014 and December 31, 2013 are as follows (in thousands):
			September 30,				December 31,
			2014				2013
	Total assets
		Carolinas	$	319,083			$	257,230
		Chicago/Milwaukee	417,134				413,585
		Houston	434,835				380,248
		Lehigh/Central PA	993,699				938,824
		Minnesota	352,447				335,613
		Orlando	255,961				253,888
		Philadelphia	350,342				316,810
		Richmond/Hampton Roads	248,186				250,008
		South Florida	393,910				380,138
		Southeastern PA	711,190				695,966
		Tampa	335,229				337,300
		United Kingdom	241,362				247,537
		Other	1,528,019				1,735,393
	Segment-level total assets		6,581,397				6,542,540
		Corporate Other	79,445				233,020
	Total assets		$	6,660,842			$	6,775,560

Accounting_for_the_Impairment_1

Accounting for the Impairment or Disposal of Long-Lived Assets (Tables)	9 Months Ended
	Sep. 30, 2014
Disposal Group, Including Discontinued Operation, Long Lived Assets [Abstract]	'
Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures [Table Text Block]	'
	A summary of the results of operations for the Portfolio Sale and other properties classified as discontinued operations through the respective disposition dates is as follows (in thousands):
			For the Three Months Ended						For the Nine Months Ended
			September 30, 2014			September 30, 2013			September 30, 2014			September 30, 2013
	Portfolio Sale
		Revenues	$	9		$	27,585		$	4,728		$	81,385
		Operating expenses	86			(10,606		)	(2,233		)	(29,155		)
		Interest and other income	3			66			40			172
		Interest expense	—			(3,830		)	(557		)	(11,550		)
		Depreciation and amortization	—			(6,798		)	—			(21,403		)
		Income before (loss) gain on property dispositions	98			6,417			1,978			19,449
		(Loss) gain on property dispositions	(35		)	—			46,086			—
		Income from discontinued operations - Portfolio Sale	63			6,417			48,064			19,449
		Noncontrolling interest	(1		)	(158		)	(1,130		)	(558		)
		Income from discontinued operations available to common shareholders - Portfolio Sale	62			6,259			46,934			18,891
		Add back noncontrolling interest	1			158			1,130			558
		Income from discontinued operations - Portfolio Sale	63			6,417			48,064			19,449
		Income from discontinued operations - other properties	73			127			212			50,559
		Income from discontinued operations	$	136		$	6,544		$	48,276		$	70,008

Noncontrolling_Interest_Operat1

Noncontrolling Interest - Operating Partnership/Limited Partners' Equity - Preferred Units (Tables)	9 Months Ended
	Sep. 30, 2014
Temporary Equity [Line Items]	'
Schedule of Temporary Equity [Table Text Block]	'
	As of September 30, 2014, the following cumulative preferred units of the Operating Partnership were outstanding:
	ISSUE	AMOUNT		UNITS	LIQUIDATION	DIVIDEND
					PREFERENCE	RATE
		(in 000’s)
	Series I-2	$	7,537	301	$25	6.25	%

Disclosure_of_Fair_Value_of_Fi1

Disclosure of Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2014
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, 2013 and September 30, 2014 (in thousands):
		Mortgage Loans				Unsecured Notes
		Carrying Value		Fair Value		Carrying Value		Fair Value
	As of December 31, 2013	$	545,306	$	573,944	$	2,708,213	$	2,764,831
	As of September 30, 2014	$	534,547	$	550,722	$	2,508,886	$	2,634,931

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2014
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, 2014, were as follows (in thousands):
	Year	Amount
	2014	$	102
	2015	428
	2016	447
	2017	447
	2018	447
	2019 through 2034	6,173
	Total	$	8,044

Supplemental_Disclosure_to_Sta1

Supplemental Disclosure to Statements of Cash Flows (Tables)	9 Months Ended
	Sep. 30, 2014
Supplemental Cash Flow Information [Abstract]	'
Supplemental Disclosure to Statements of Cash Flows	'
	The following are supplemental disclosures to the statements of cash flows for the nine months ended September 30, 2014 and 2013 (amounts in thousands):
		2014			2013
	Write-off of fully depreciated property and deferred costs	$	31,322		$	23,180
	Write-off of depreciated property and deferred costs due to sale	$	132,707		$	49,618
	Unrealized losses on cash flow hedge	$	(990	)	$	—
	Write-off of origination costs relating to preferred unit redemptions	$	—		$	1,236
	Increase in investments in and advances to unconsolidated joint ventures due to disposition activity	$	(11,948	)	$	—
	Changes in accrued development capital expenditures	$	7,854		$	12,869

Organization_and_Basis_of_Pres2

Organization and Basis of Presentation (Narrative) (Details)	Sep. 30, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Ownership interest in operating partnership - Limited Partnership	97.70%

Income_per_Common_Share_of_the2

Income per Common Share of the Trust (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]	'	'	'	'
Income from continuing operations net of noncontrolling interest	$34,290	$22,316	$88,430	$72,048
Discontinued operations net of noncontrolling interest	133	6,383	47,142	67,999
Net income available to common shareholders	$34,423	$28,699	$135,572	$140,047
Weighted Average Number of Shares Outstanding, Diluted [Abstract]	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	147,422	135,628	146,987	124,889
Dilutive shares for long-term compensation plans	666	700	674	766
Weighted Average Number of Shares Outstanding, Diluted	148,088	136,328	147,661	125,655
Common shares [Member]	'	'	'	'
Earnings Per Share, Basic [Abstract]	'	'	'	'
Income from Continuing Operations, Per Basic Share	$0.23	$0.16	$0.60	$0.58
Income from Discontinued Operations, Per Basic Share	$0	$0.05	$0.32	$0.54
Income per common share - basic	$0.23	$0.21	$0.92	$1.12
Earnings Per Share, Diluted [Abstract]	'	'	'	'
Income from Continuing Operations, Per Diluted Share	$0.23	$0.16	$0.60	$0.57
Income from Discontinued Operations, Per Diluted Share	$0	$0.05	$0.32	$0.54
Income per common share - diluted	$0.23	$0.21	$0.92	$1.11

Income_per_Common_Share_of_the3

Income per Common Share of the Trust Income per Common Share of the Trust, Anti-dilutive (Details) (Stock Option [Member])	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Stock Option [Member]	'	'	'	'
Antidilutive Options Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Antidilutive Options Excluded from Computation of Earnings Per Share	1,183,000	994,000	850,000	959,000

Income_per_Common_Share_of_the4

Income per Common Share of the Trust Income per Common Share of the Trust, Dilutive (Details) (Stock Option [Member], Common shares [Member])	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013
Stock Option [Member] | Common shares [Member]	'	'	'
Stock Option Exercises [Line Items]	'	'	'
Amount of Options Exercises in Period	0	43,000	504,000

Income_per_Common_Unit_of_the_2

Income per Common Unit of the Operating Partnership Income per Common Unit of the Operating Partnership, Diluted (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]	'	'	'	'
Income from continuing operations net of noncontrolling interest	$34,290	$22,316	$88,430	$72,048
Discontinued operations	136	6,544	48,276	70,008
Net income available to common shareholders	34,423	28,699	135,572	140,047
Weighted Average Number of Shares Outstanding, Diluted [Abstract]	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	147,422	135,628	146,987	124,889
Dilutive units for long-term compensation plans	666	700	674	766
Weighted Average Number of Shares Outstanding, Diluted	148,088	136,328	147,661	125,655
Liberty Property Limited Partnership [Member]	'	'	'	'
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]	'	'	'	'
Income from continuing operations net of noncontrolling interest	35,231	22,998	90,914	77,433
Less: Preferred unit distributions	-118	-118	-354	-2,001
Excess of preferred unit redemption over carrying amount	'	'	0	-1,236
Income from Continuing Operations available to Common Unitholders	35,113	22,880	90,560	74,196
Discontinued operations	136	6,544	48,276	70,008
Net income available to common shareholders	$35,249	$29,424	$138,836	$144,204
Weighted Average Number of Shares Outstanding, Diluted [Abstract]	'	'	'	'
Weighted Average Number of Shares Outstanding, Basic	150,976	139,320	150,541	128,595
Dilutive units for long-term compensation plans	666	700	674	766
Weighted Average Number of Shares Outstanding, Diluted	151,642	140,020	151,215	129,361
Liberty Property Limited Partnership [Member] | Common Units [Member]	'	'	'	'
Earnings Per Share, Basic [Abstract]	'	'	'	'
Income from Continuing Operations, Per Basic Share	$0.23	$0.16	$0.60	$0.58
Income from Discontinued Operations, Per Basic Share	$0	$0.05	$0.32	$0.54
Income per common share - basic	$0.23	$0.21	$0.92	$1.12
Earnings Per Share, Diluted [Abstract]	'	'	'	'
Income from Continuing Operations, Per Diluted Share	$0.23	$0.16	$0.60	$0.57
Income from Discontinued Operations, Per Diluted Share	$0	$0.05	$0.32	$0.54
Income per common share - diluted	$0.23	$0.21	$0.92	$1.11

Income_per_Common_Unit_of_the_3

Income per Common Unit of the Operating Partnership Income per Common Unit of the Operating Partnership, Anti-dilutive Options (Details) (Stock Option [Member])	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Antidilutive Options Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Antidilutive Options Excluded from Computation of Earnings Per Share	1,183,000	994,000	850,000	959,000
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	1,183,000	994,000	850,000	959,000

Income_per_Common_Unit_of_the_4

Income per Common Unit of the Operating Partnership Income per Common Unit of the Operations Partnership, Dilutive Options (Details) (Liberty Property Limited Partnership [Member], Stock Option [Member], Common Units [Member])	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013
Liberty Property Limited Partnership [Member] | Stock Option [Member] | Common Units [Member]	'	'	'
Stock Option Exercises [Line Items]	'	'	'
Amount of Options Exercises in Period	0	43,000	504,000

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Foreign Currency Translation:	'	'	'	'	'
Beginning balance	'	'	$8,592	$3,195	'
Translation adjustment	'	'	-5,189	115	'
Ending balance	3,403	3,310	3,403	3,310	'
Net unrealized gain on derivative instruments:	'	'	'	'	'
Beginning balance	'	'	1,584	0	'
Unrealized losses	666	0	-990	0	'
Ending balance	594	0	594	0	'
Total accumulated other comprehensive income	3,997	3,310	3,997	3,310	'
Less: portion included in noncontrolling interest - operating partnership	-290	-272	-290	-272	'
Total accumulated other comprehensive income included in shareholders' equity	$3,707	$3,038	$3,707	$3,038	$9,742

Segment_Information_Performanc

Segment Information - Performance of the Reportable Segments Based on Property Level Operating Income (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	$198,356,000		$155,348,000		$588,946,000		$453,498,000
Net operating income	66,330,000		52,413,000		188,145,000		150,791,000
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]	'		'		'		'
Interest expense	-37,958,000		-33,542,000		-115,635,000		-89,414,000
Depreciation and amortization expense	'		'		-176,207,000		-137,302,000
(Loss) gain on property dispositions	-20,000		0		1,879,000		0
Equity in earnings of unconsolidated joint ventures	1,592,000		650,000		7,297,000		3,973,000
General and administrative expense	-14,748,000		-17,217,000		-48,077,000		-53,466,000
Income taxes	-859,000		-629,000		-2,083,000		-1,780,000
Income from continuing operations	35,315,000		23,404,000		91,388,000		77,839,000
Intersegment Eliminations [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	0		0		0		0
Operating Segments [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	198,350,000		183,237,000		593,962,000		539,757,000
Net operating income	124,521,000		109,293,000		367,264,000		318,582,000
Operating Segments [Member] | Carolinas [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	9,479,000		7,626,000		26,282,000		22,213,000
Net operating income	6,570,000		5,182,000		18,006,000		15,035,000
Operating Segments [Member] | Chicago Milwaukee [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	8,004,000		3,067,000		24,727,000		9,230,000
Net operating income	5,382,000		2,163,000		15,518,000		6,149,000
Operating Segments [Member] | Houston [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	12,833,000		9,481,000		36,828,000		26,833,000
Net operating income	7,510,000		5,426,000		21,794,000		15,735,000
Operating Segments [Member] | Lehigh Central PA [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	30,034,000		24,981,000		87,853,000		74,339,000
Net operating income	21,634,000		17,204,000		60,647,000		50,422,000
Operating Segments [Member] | Minnesota [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	13,925,000		15,591,000		41,217,000		46,319,000
Net operating income	6,575,000		7,289,000		19,964,000		22,563,000
Operating Segments [Member] | Orlando [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	8,463,000		7,583,000		24,519,000		23,156,000
Net operating income	5,411,000		5,128,000		16,257,000		15,504,000
Operating Segments [Member] | Philadelphia [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	8,303,000		7,633,000		26,402,000		23,027,000
Net operating income	6,736,000		5,919,000		20,247,000		16,869,000
Operating Segments [Member] | Richmond Hampton Roads [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	10,358,000		9,959,000		30,542,000		29,899,000
Net operating income	6,144,000		5,899,000		18,118,000		17,978,000
Operating Segments [Member] | South Florida [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	12,012,000		8,798,000		36,028,000		26,032,000
Net operating income	6,647,000		4,735,000		21,066,000		14,168,000
Operating Segments [Member] | Southeastern PA [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	36,087,000		41,251,000		110,833,000		122,694,000
Net operating income	20,516,000		23,754,000		60,175,000		68,622,000
Operating Segments [Member] | Tampa [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	13,597,000		12,767,000		40,001,000		38,849,000
Net operating income	8,213,000		7,916,000		25,142,000		24,522,000
Operating Segments [Member] | United Kingdom [Member] | European Union [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	4,111,000		1,400,000		12,430,000		3,620,000
Net operating income	2,468,000		123,000		8,716,000		-331,000
Operating Segments [Member] | Other Segments [Member] | North America [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	31,144,000		33,100,000		96,300,000		93,546,000
Net operating income	20,715,000		18,555,000		61,614,000		51,346,000
Discontinued Operations [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	-9,000		-28,007,000		-4,728,000		-86,604,000
Corporate, Non-Segment [Member]	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Operating revenue	15,000		118,000		-288,000		345,000
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]	'		'		'		'
Interest expense	-37,958,000	[1]	-37,412,000	[1]	-116,192,000	[1]	-101,632,000	[1]
Depreciation and amortization expense	-44,538,000	[1],[2]	-29,963,000	[1],[2]	-133,636,000	[1],[2]	-88,330,000	[1],[2]
(Loss) gain on property dispositions	-20,000		0		1,879,000		0
Equity in earnings of unconsolidated joint ventures	1,592,000		650,000		7,297,000		3,973,000
General and administrative expense	-8,556,000	[1],[2]	-12,394,000	[1],[2]	-29,189,000	[1],[2]	-35,215,000	[1],[2]
Discontinued operations excluding gain on property dispositions	-98,000		-6,515,000		-1,985,000		-20,641,000
Income taxes	-821,000	[2]	-636,000	[2]	-1,966,000	[2]	-1,772,000	[2]
Other	$1,193,000		$381,000		($2,084,000)		$2,874,000
[1]	Includes activity on discontinued operations.
[2]	Excludes costs which are included in determining segment-level net operating income.

Segment_Information_Total_Asse

Segment Information - Total Assets by Segment (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]	'	'
Assets	$6,660,842,000	$6,775,560,000
Operating Segments [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	6,581,397,000	6,542,540,000
Corporate, Non-Segment [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	79,445,000	233,020,000
North America [Member] | Operating Segments [Member] | Carolinas [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	319,083,000	257,230,000
North America [Member] | Operating Segments [Member] | Chicago Milwaukee [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	417,134,000	413,585,000
North America [Member] | Operating Segments [Member] | Houston [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	434,835,000	380,248,000
North America [Member] | Operating Segments [Member] | Lehigh Central PA [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	993,699,000	938,824,000
North America [Member] | Operating Segments [Member] | Minnesota [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	352,447,000	335,613,000
North America [Member] | Operating Segments [Member] | Orlando [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	255,961,000	253,888,000
North America [Member] | Operating Segments [Member] | Philadelphia [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	350,342,000	316,810,000
North America [Member] | Operating Segments [Member] | Richmond Hampton Roads [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	248,186,000	250,008,000
North America [Member] | Operating Segments [Member] | South Florida [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	393,910,000	380,138,000
North America [Member] | Operating Segments [Member] | Southeastern PA [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	711,190,000	695,966,000
North America [Member] | Operating Segments [Member] | Tampa [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	335,229,000	337,300,000
North America [Member] | Operating Segments [Member] | Other Segments [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	1,528,019,000	1,735,393,000
European Union [Member] | Operating Segments [Member] | United Kingdom [Member]	'	'
Segment Reporting Information [Line Items]	'	'
Assets	$241,362,000	$247,537,000

Segment_Information_Building_A

Segment Information Building Acquisitions and Dispositions (Details) (USD $)	3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2014
	bldg	bldg
Land, Buildings and Improvements [Member]	'	'
Acquisitions [Abstract]	'	'
Number of real estate properties acquired	1	9
Total purchase price	$6.80	$97.70
Dispositions [Abstract]	'	'
Proceeds from Sale of Property	'	366.9
Number of Real Estate Properties Sold	0	52
Land [Member]	'	'
Dispositions [Abstract]	'	'
Acres of land sold	19	19
Liberty Venture I, LP [Member]	'	'
Dispositions [Abstract]	'	'
Equity Method Investment, Ownership Percentage	25.00%	25.00%
Liberty Venture I, LP [Member] | Equity Method Investee [Member] | Land, Buildings and Improvements [Member]	'	'
Dispositions [Abstract]	'	'
Proceeds from Sale of Property	'	$32.20
Number of Real Estate Properties Sold	'	3

Accounting_for_the_Impairment_2

Accounting for the Impairment or Disposal of Long-Lived Assets (Details) (USD $)

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Nov. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Jan. 31, 2014

Jan. 31, 2014

Jan. 31, 2014

Jan. 31, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Discontinued Operations [Member]

Discontinued Operations [Member]

Discontinued Operations [Member]

Discontinued Operations [Member]

Other Segments [Member]

Portfolio Sale, Total [Member]

Portfolio Sale, Total [Member]

Portfolio Sale, Total [Member]

Portfolio Sale, Total [Member]

Portfolio Sale, Total [Member]

Portfolio Sale, Total [Member]

Other Properties [Member]

Other Properties [Member]

Other Properties [Member]

Other Properties [Member]

Portfolio Sale, first settlement [Member]

Portfolio Sale, Second Settlement [Member]

Portfolio Sale, Second Settlement [Member]

Portfolio Sale, Second Settlement [Member]

Portfolio Sale, Second Settlement [Member]

Land, Buildings and Improvements [Member]

Land, Buildings and Improvements [Member]

Land, Buildings and Improvements [Member]

Land, Buildings and Improvements [Member]

sqft

sqft

Discontinued Operations [Member]

Discontinued Operations [Member]

Discontinued Operations [Member]

Discontinued Operations [Member]

Discontinued Operations [Member]

Discontinued Operations [Member]

Discontinued Operations [Member]

Discontinued Operations [Member]

sqft

Other Segments [Member]

Other Segments [Member]

Southeastern PA [Member]

bldg

bldg

Not Discontinued Operations [Member]

Other Segments [Member]

properties

properties

Maryland [Member]

New Jersey [Member]

properties

bldg

Not Discontinued Operations [Member]

acre

sqft

properties

sqft

bldg

properties

sqft

acre

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of Real Estate Properties

'

'

'

'

'

'

'

'

'

'

97

'

'

'

'

'

'

'

'

49

'

23

24

1

'

'

'

'

Area of Real Estate Property

'

'

'

'

'

'

'

'

75,000

'

6,600,000

'

'

'

'

'

'

'

'

4,000,000

'

1,400,000

1,200,000

37,000

'

'

'

'

Significant Disposals, Sale Proceeds

'

'

'

'

'

'

'

'

'

'

$697,300,000

'

'

'

'

'

'

'

'

$367,700,000

$329,600,000

'

'

'

'

'

'

'

Number of Real Estate Settlements

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Acres of land sold

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

140

'

19

'

'

'

'

'

'

Number of Real Estate Properties Sold

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

52

0

4

Proceeds from Sale of Property

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

126,000,000

'

'

'

'

'

'

'

'

366,900,000

'

37,300,000

Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Revenues

'

'

'

'

'

'

'

'

'

'

'

9,000

27,585,000

4,728,000

81,385,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Operating expenses

'

'

'

'

'

'

'

'

'

'

'

86,000

-10,606,000

-2,233,000

-29,155,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest and other income

'

'

'

'

'

'

'

'

'

'

'

3,000

66,000

40,000

172,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest expense

'

'

'

'

'

'

'

'

'

'

'

0

-3,830,000

-557,000

-11,550,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Depreciation and Amortization

'

'

'

'

'

'

'

'

'

'

'

0

-6,798,000

0

-21,403,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Income before (loss) gain on property dispositions

'

'

'

'

'

'

'

'

'

'

'

98,000

6,417,000

1,978,000

19,449,000

'

'

'

'

'

'

'

'

'

'

'

'

'

(Loss) gain on property dispositions

38,000

29,000

46,291,000

49,367,000

'

'

'

'

'

'

'

-35,000

0

46,086,000

0

'

'

'

'

'

'

'

'

'

'

'

'

'

Income from discontinued operations

136,000

6,544,000

48,276,000

70,008,000

136,000

6,544,000

48,276,000

70,008,000

'

'

'

63,000

6,417,000

48,064,000

19,449,000

73,000

127,000

212,000

50,559,000

'

'

'

'

'

'

'

'

'

Noncontrolling Interest

'

'

'

'

'

'

'

'

'

'

'

-1,000

-158,000

-1,130,000

-558,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Income from discontinued operations available to common shareholders

'

'

'

'

'

'

'

'

'

'

'

62,000

6,259,000

46,934,000

18,891,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Discontinued Operation, Additional Disclosures [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Disposal Group, Including Discontinued Operation, Operating Cash Flows

'

'

'

'

'

'

'

'

'

'

'

-1,500,000

11,500,000

-4,300,000

39,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Disposal Group, Including Discontinued Operations, Investing Cash Flows

'

'

'

'

'

'

'

'

'

'

'

($42,000)

($3,400,000)

$313,100,000

($11,100,000)

'

'

'

'

'

'

'

'

'

'

'

'

'

Noncontrolling_Interests_of_th1

Noncontrolling Interests of the Trust- Narrative (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, except Share data, unless otherwise specified
Redeemable Noncontrolling Interest [Line Items]	'	'
Common units, units outstanding not held by the trust	3,553,566	3,556,556
Reportable Legal Entities [Member] | Liberty Property Limited Partnership [Member]	'	'
Redeemable Noncontrolling Interest [Line Items]	'	'
Market value of common units based on closing price	118.2	'

Limited_Partners_Equity_of_the1

Limited Partners' Equity of the Operating Partnership - Narrative (Details) (Liberty Property Limited Partnership [Member], USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, except Share data, unless otherwise specified
Liberty Property Limited Partnership [Member]	'	'
Limited Partners' Capital Account [Line Items]	'	'
Limited Partners' Capital Account, Units Outstanding	3,553,566	3,556,556
market value of the outstanding common units	$118.20	'

Noncontrolling_Interest_Operat2

Noncontrolling Interest - Operating Partnership/Limited Partners' Equity - Preferred Units (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Temporary Equity [Line Items]	'	'
Cumulative redeemable preferred units of the Operating Partnership outstanding	$7,537	7,537
Series I 2 [Member]	'	'
Temporary Equity [Line Items]	'	'
Cumulative redeemable preferred units of the Operating Partnership outstanding	$7,537	'
Units	301,483	301,483
Liquidation Preference	$25	'
Dividend Rate	6.25%	'

Indebtedness_Details

Indebtedness (Details) (USD $)	9 Months Ended			3 Months Ended	9 Months Ended		9 Months Ended		9 Months Ended	3 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Mar. 31, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014
	Y		Line of Credit [Member]	Line of Credit [Member]	Line of Credit [Member]	Total Debt to Total Assets Ratio [Member]	EBITDA to Fixed Charges Ratio [Member]	Unsecured Debt to Unencumbered Asset Ratio [Member]	Unencumbered Net Operating Income to Unsecured Interest Expense [Member]	Unsecured Notes
			Old Credit Facility [Member]	New Credit Facility [Member]	New Credit Facility [Member]	Line of Credit [Member]	Line of Credit [Member]	Line of Credit [Member]	Line of Credit [Member]	Senior Notes [Member]
						New Credit Facility [Member]		New Credit Facility [Member]	New Credit Facility [Member]	5.65% Senior Note [Member]
Credit Facility [Abstract]	'	'	'	'	'	'	'	'	'	'
Line of Credit Facility, Maximum Borrowing Capacity	'	'	$500,000,000	$800,000,000	$800,000,000	'	'	'	'	'
Length of Maturity Extension	1	'	'	'	'	'	'	'	'	'
Debt Instrument, Basis Spread on Variable Rate	'	'	'	1.05%	'	'	'	'	'	'
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	'	'	'	0.20%	'	'	'	'	'	'
Line of Credit Facility, Competitive Bid Option, Percentage	'	'	'	'	50.00%	'	'	'	'	'
Borrowed Funds	'	'	'	'	'	0.6	'	'	'	'
Assets	6,660,842,000	6,775,560,000	'	'	'	1	'	'	'	'
Line of Credit Facility, Covenant Terms, Earnings before Interest, Taxes, Depreciation and Amortization to Fixed Charges Ratio	'	'	'	'	'	'	1.5	'	'	'
Line of Credit Facility, Unsecured Debt to Unencumbered Asset Value, Maximum	'	'	'	'	'	'	'	60.00%	'	'
Line of Credit Facility, Unencumbered Net Operating Income to Unsecured Interest Expense, Minimum	'	'	'	'	'	'	'	'	175.00%	'
Unsecured Notes [Abstract]	'	'	'	'	'	'	'	'	'	'
Interest Rate	'	'	'	'	'	'	'	'	'	5.65%
Repayment of unsecured note	'	'	'	'	'	'	'	'	'	$200,000,000

Disclosure_of_Fair_Value_of_Fi2

Disclosure of Fair Value of Financial Instruments (Details) (Fair Value, Inputs, Level 3 [Member], USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Carrying Value | Mortgage Loans	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Long-term Debt, Fair Value	$534,547	$545,306
Carrying Value | Unsecured Notes	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Long-term Debt, Fair Value	2,508,886	2,708,213
Fair Value | Mortgage Loans	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Long-term Debt, Fair Value	550,722	573,944
Fair Value | Unsecured Notes	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Long-term Debt, Fair Value	$2,634,931	$2,764,831

Investment_in_Unconsolidated_J1

Investment in Unconsolidated Joint Ventures (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Jun. 30, 2014	Jun. 30, 2014	Sep. 30, 2014
			Comcast Innovation and Technology Center [Member]	Comcast Innovation and Technology Center [Member]	Comcast corporation lease [Member]	Comcast corporation lease [Member]
			room	investment	Lease Agreements [Member]	Lease Agreements [Member]
			story		Comcast Innovation and Technology Center [Member]	Comcast Innovation and Technology Center [Member]
			sqft			sqft
Comcast Innovative and Technology Center [Abstract]	'	'	'	'	'	'
Number of equity method investments	'	'	'	2	'	'
Number of stories in a high-rise building	'	'	59	'	'	'
Net Rentable Area	'	'	1,300,000	'	'	982,275
Number of hotel rooms	'	'	220	'	'	'
Total anticipated development cost	'	'	$921,000,000	'	'	'
Anticipated investment in joint ventures	'	'	184,000,000	'	'	'
Equity Method Investment, Ownership Percentage	'	'	20.00%	'	'	'
Real Estate Investments, Joint Ventures	202,570,000	179,655,000	17,400,000	'	'	'
Development in Process	$250,506,000	$209,187,000	$85,500,000	'	'	'
Length of Lease	'	'	'	'	'20 years	'
Percent of net rentable area	'	'	'	'	'	73.40%

Investment_in_Unconsolidated_J2

Investment in Unconsolidated Joint Ventures Investment in Unconsolidated Joint Ventures - Related Party (Details) (USD $)	3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2014
Comcast Innovation and Technology Center [Member] | Equity Method Investee [Member]	'	'
Comcast Innovative and Technology Center [Abstract]	'	'
developers fee	$0.70	$0.70
Liberty Venture I, LP [Member]	'	'
Liberty Venture I LP [Abstract]	'	'
Equity Method Investment, Ownership Percentage	25.00%	25.00%
Land, Buildings and Improvements [Member]	'	'
Liberty Venture I LP [Abstract]	'	'
Number of real estate properties acquired	1	9
Total purchase price	6.8	97.7
Land, Buildings and Improvements [Member] | Liberty Venture I, LP [Member] | General Partner [Member]	'	'
Liberty Venture I LP [Abstract]	'	'
Number of real estate properties acquired	'	3
Net rentable area acquired	'	603,000
Total purchase price	'	$32.20

Business_Combination_Details

Business Combination (Details) (Cabot Industrial Value Fund III [Member], USD $)	0 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Oct. 08, 2013	Dec. 31, 2013
	sqft
Business Acquisition [Line Items]	'	'
Business Acquisition, Effective Date of Acquisition	'	8-Oct-13
Business Acquisition, Name of Acquired Entity	'	'Cabot Industrial Fund III Operating Partnership, L.P.
Business Acquisition, Percentage of Voting Interests Acquired	100.00%	'
Area of Real Estate Property	23,000,000	'
Business Combination, Consideration Transferred	$1,469	'
Industrial Property [Member]	'	'
Business Acquisition [Line Items]	'	'
Number of Real Estate Properties	177	'
Mortgages [Member]	'	'
Business Acquisition [Line Items]	'	'
Business Combination, Consideration Transferred, Liabilities Incurred	$229.80	'

Derivative_Instruments_Details

Derivative Instruments (Details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013
Interest Rate Derivatives [Abstract]	'	'	'
Number of interest rate swap contracts	3	3	'
aggregate notional amount	$104,100,000	$104,100,000	$105,200,000
Termination value of interest rate swap, including accrued interest	8,300,000	8,300,000	'
Interest Rate Cash Flow Hedges [Abstract]	'	'	'
Change in fair value of swaps as a decrease to other comprehensive income	-666,000	990,000	'
Amount of loss reclassified into interest expense from AOCI	367,000	1,100,000	'
Ineffective portion of the change in the fair value of swaps as an adjustment to interest expense	-13,000	42,000	'
Fair value of interest rate swaps	8,000,000	8,000,000	8,400,000
Amount estimated to be reclassified from accumulated other comprehensive income as an adjustment to interest expense	$1,300,000	$1,300,000	'

Commitments_and_Contingencies_1

Commitments and Contingencies - Future Minimum Rental Payments (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Commitments and Contingencies Disclosure [Abstract]	'	'	'	'
2014	$102,000	'	$102,000	'
2015	428,000	'	428,000	'
2016	447,000	'	447,000	'
2017	447,000	'	447,000	'
2018	447,000	'	447,000	'
2019 through 2034	6,173,000	'	6,173,000	'
Total	8,044,000	'	8,044,000	'
Other Expenses [Abstract]	'	'	'	'
Operating ground lease expense	$114,000	$42,000	$289,000	$125,000

Commitments_and_Contingencies_2

Commitments and Contingencies Commitments and Contingencies - Loss Contingencies (Details) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Legal Matters [Abstract]	'
Loss Contingency, Pending Claims, Number	0
Other [Abstract]	'
Letter of credit obligations	$8.90

Commitments_and_Contingencies_3

Commitments and Contingencies Commitments and Contingencies - Supply Commitments (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Supply Commitment [Line Items]	'	'
Development in Process	$250,506,000	$209,187,000
Construction in Progress [Member]	'	'
Supply Commitment [Line Items]	'	'
Number of Real Estate Properties	22	'
Area of Real Estate Property	4,700,000	'
Total anticipated development cost	428,700,000	'
Deferred Costs, Leasing, Gross	6,600,000	'
Development Not Yet Commenced [Member]	'	'
Supply Commitment [Line Items]	'	'
Total anticipated development cost	20,400,000	'
Buildings and land parcels [Member]	'	'
Supply Commitment [Line Items]	'	'
Remaining amount committed or obligated to pay for the benefit of current or future tenants	12,800,000	'
Maximum [Member] | Tenant Improvements [Member]	'	'
Supply Commitment [Line Items]	'	'
Remaining amount committed or obligated to pay for the benefit of current or future tenants	$52,100,000	'

Commitments_and_Contingencies_4

Commitments and Contingencies Commitments and Contingencies - Purchase Commitments (Details) (Land Purchases [Member], USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Land Purchases [Member]	'
Long-term Purchase Commitment [Line Items]	'
Remaining amount commitment to future land purchases	$56.30

Supplemental_Disclosure_to_Sta2

Supplemental Disclosure to Statements of Cash Flows (Details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Supplemental Cash Flow Information [Abstract]	'	'
Write off of fully depreciated property and deferred costs	$31,322	$23,180
Write off of depreciated property and deferred costs due to sale	132,707	49,618
Unrealized losses on cash flow hedge, non cash transaction	-990	0
Write-off of preferred units costs due to redemption	0	1,236
Increase in investments in and advances to unconsolidated joint ventures due to disposition activity	-11,948	0
Changes in accrued development capital expenditures	$7,854	$12,869