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Properties, net (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014
Investments in real estate
Operating properties, net		$ 2,896,809	$ 2,751,488
Greater Philadelphia
Investments in real estate
Depreciation expense on reclassified assets	$ 12,900
Operating properties, net
Investments in real estate
Less: accumulated depreciation		(723,470)	(703,083)
Operating properties, net | Land
Investments in real estate
Gross		460,268	439,355
Operating properties, net | Buildings and improvements
Investments in real estate
Gross		$ 3,160,011	$ 3,015,216

X

- Definition

Additional depreciation expense recognized resulting from a change in the useful life of the disclosed asset.

+ References

No definition available.

+ Details

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X

- Definition

Amount, before accumulated depreciation, of real estate investments for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 205



-SubTopic 10



-Section S99



-Paragraph 6



-Subparagraph (SX 210.5-04.(c) Schedule III)



-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674



Reference 2: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 970



-SubTopic 360



-Section S99



-Paragraph 1



-Subparagraph (SX 210.12-28.4)



-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024



Reference 3: http://www.xbrl.org/2003/role/presentationRef



-Publisher SEC



-Name Regulation S-X (SX)



-Number 210



-Section 04



-Paragraph c



-Subparagraph Schedule III



-Article 5



Reference 4: http://www.xbrl.org/2003/role/presentationRef



-Publisher SEC



-Name Regulation S-X (SX)



-Number 210



-Section 28



-Article 12

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X

- Definition

The cumulative amount of depreciation for real estate property held for investment purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 944



-SubTopic 210



-Section S99



-Paragraph 1



-Subparagraph (SX 210.7-03.1(3))



-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910



Reference 2: http://www.xbrl.org/2003/role/presentationRef



-Publisher SEC



-Name Regulation S-X (SX)



-Number 210



-Section 03



-Paragraph 1



-Article 7

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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X

- Definition

Carrying amount of income producing properties held for rental.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 944



-SubTopic 210



-Section S99



-Paragraph 1



-Subparagraph (SX 210.7-03.1(d))



-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Details

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- Details

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X

- Details

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- Details

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