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Real Estate Investments - Summary of Properties Classified as Held for Sale Included in Continuing Operations (Parenthetical) (Details) | Sep. 30, 2017 ft² property
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Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |
Number of Properties | 97
Office Properties [Member] |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |
Number of Properties | 82
Held for Sale Properties Included in Continuing Operations [Member] |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |
Number of Properties | 6
Held for Sale Properties Included in Continuing Operations [Member] | Pennsylvania Suburbs [Member] | Office Properties [Member] |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |
Number of Properties | 6
Held for Sale Properties Included in Continuing Operations [Member] | Pennsylvania Suburbs [Member] | 630 Allendale Road - Office [Member] | Office Properties [Member] |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |
Rentable Square Feet | ft² | 150,000
Held for Sale Properties Included in Continuing Operations [Member] | Pennsylvania Suburbs [Member] | Newtown Square - Office [Member] | Office Properties [Member] |
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] |
Rentable Square Feet | ft² | 252,802
Number of Properties | 5

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