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Investment in Unconsolidated Real Estate Ventures (Textual) (Details) |  |  |  |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Aug. 01, 2018 USD ($) | Jun. 26, 2018 USD ($) | Jan. 10, 2018 USD ($) property | Jan. 05, 2018 USD ($) ft² | Sep. 30, 2018 USD ($) ft² a Real_Estate_Investment Apartment_unit | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) ft² a Real_Estate_Investment Apartment_unit | Sep. 30, 2017 USD ($) | Dec. 31, 2017 USD ($)
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Investment in Real Estate Ventures, equity method |  |  |  |  | $ 167,782,000 |  | $ 167,782,000 |  | $ 194,621,000
Accounts receivable |  |  |  |  | 13,871,000 |  | 13,871,000 |  | 17,938,000
Debt, net |  |  |  |  | $ 660,041,000 |  | $ 660,041,000 |  | 766,420,000
Area of real estate property | ft² |  |  |  |  | 16,462,764 |  | 16,462,764 |  |
Net gain on Real Estate Venture transactions |  |  |  |  | $ 0 | $ 13,758,000 | $ 37,263,000 | $ 28,340,000 |
Proceeds from real estate venture sales |  |  |  |  |  |  | 42,953,000 | 59,022,000 |
Evo at Cira Disposition [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Sale of ownership interest percentage |  |  | 50.00% |  |  |  |  |  |
Net gain on Real Estate Venture transactions |  |  | $ 25,700,000 |  |  |  |  |  |
Number of property units sold | property |  |  | 345 |  |  |  |  |  |
Sales Price |  |  | $ 197,500,000 |  |  |  |  |  |
Proceeds from real estate venture sales |  |  | 43,000,000.0 |  |  |  |  |  |
Cost of equity method investment |  |  | 17,300,000 |  |  |  |  |  |
Philadelphia [Member] | Pennsylvania [Member] | Evo at Cira Disposition [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Principal balance of secured loan |  |  | $ 110,900,000 |  |  |  |  |  |
Secured Debt [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Real estate property debt |  |  |  |  | 324,886,000 |  | 324,886,000 |  | 320,107,000
Third Party Management Fees, Labor Reimbursement and Leasing [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Management fees |  |  |  |  | $ 4,944,000 | 6,918,000 | $ 17,531,000 | 20,483,000 |
Office Properties [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  | 38,260 |  | 38,260 |  |
Area of real estate property | ft² |  |  |  |  | 13,673,405 |  | 13,673,405 |  |
Sales Price |  |  |  |  | $ 2,000,000 |  | $ 2,000,000 |  |
Real Estate Venture [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Accounts receivable |  |  |  |  | 1,200,000 |  | 1,200,000 |  | $ 900,000
Real Estate Venture [Member] | Third Party Management Fees, Labor Reimbursement and Leasing [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Management fees |  |  |  |  | 1,400,000 | 1,700,000 | 4,000,000.0 | 4,900,000 |
Real Estate Venture [Member] | Lease Commission Income [Member] | Third Party Management Fees, Labor Reimbursement and Leasing [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Management fees |  |  |  |  | $ 1,500,000 | $ 1,900,000 | $ 4,400,000 | $ 5,500,000 |
Unconsolidated Real Estate Ventures [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Number of unconsolidated investments in Real Estate Ventures | Real_Estate_Investment |  |  |  |  | 10 |  | 10 |  |
Investment in Real Estate Ventures, equity method |  |  |  |  | $ 167,800,000 |  | $ 167,800,000 |  |
Real estate ventures aggregate indebtedness to third parties |  |  |  |  | $ 664,200,000 |  | $ 664,200,000 |  |
Unconsolidated Real Estate Ventures [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  | 25.00% | 20.00% | 25.00% | 20.00% |
Unconsolidated Real Estate Ventures [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  |  | 70.00% | 70.00% | 70.00% | 70.00% |
Unconsolidated Real Estate Ventures [Member] | Six Real Estate Ventures [Member] | Office Properties [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Number of unconsolidated investments in Real Estate Ventures | Real_Estate_Investment |  |  |  |  | 6 |  | 6 |  |
Rentable Square Feet | ft² |  |  |  |  | 6,600,000 |  | 6,600,000 |  |
Unconsolidated Real Estate Ventures [Member] | Two Real Estate Ventures [Member] | Land Held For Development [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Number of unconsolidated investments in Real Estate Ventures | Real_Estate_Investment |  |  |  |  | 2 |  | 2 |  |
Acreage of land | a |  |  |  |  | 1.4 |  | 1.4 |  |
Unconsolidated Real Estate Ventures [Member] | One Real Estate Venture [Member] | Land Under Active Development [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Number of unconsolidated investments in Real Estate Ventures | Real_Estate_Investment |  |  |  |  | 1 |  | 1 |  |
Acreage of land | a |  |  |  |  | 1.3 |  | 1.3 |  |
Unconsolidated Real Estate Ventures [Member] | One Other Real Estate Venture [Member] | Residential Tower [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Number of unconsolidated investments in Real Estate Ventures | Real_Estate_Investment |  |  |  |  | 1 |  | 1 |  |
Number of Property units | Apartment_unit |  |  |  |  | 321 |  | 321 |  |
MAP Ground Lease Venture LLC [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership percentage | 50.00% |  |  |  |  |  |  |  |
Real estate ventures aggregate indebtedness to third parties | $ 180,800,000 |  |  |  |  |  |  |  |
Debt instrument maturity date | Feb. 09, 2019 |  |  |  |  |  |  |  |
MAP Ground Lease Venture LLC [Member] | Secured Debt [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Debt instrument maturity date | Aug. 01, 2023 |  |  |  |  |  |  |  |
Indebtedness to third parties, refinanced amount | $ 185,000,000.0 |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate | 2.45% |  |  |  |  |  |  |  |
MAP Ground Lease Venture LLC [Member] | Maximum [Member] | Secured Debt [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Effective interest rate | 6.00% |  |  |  |  |  |  |  |
1919 Ventures |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership percentage |  | 50.00% |  |  |  |  |  |  |
Debt, net |  | $ 44,400,000 |  |  |  |  |  |  |
Loan interest rate |  | 4.00% |  |  |  |  |  |  |
Mortgage loans scheduled maturity date |  | Jun. 25, 2023 |  |  |  |  |  |  |
Repayment of construction loan |  | $ 88,800,000 |  |  |  |  |  |  |
Construction loan, principal amount |  | 88,600,000 |  |  |  |  |  |  |
Accrued interest on construction loan |  | $ 200,000 |  |  |  |  |  |  |
1919 Ventures | LCOR/Calstrs [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership percentage |  | 50.00% |  |  |  |  |  |  |
1919 Ventures | Other Assets [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Note receivable |  | $ 44,400,000 |  |  |  |  |  |  |
Four Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership percentage |  |  |  | 35.00% |  |  |  |  |
Net gain on Real Estate Venture transactions |  |  |  | $ 11,600,000 |  |  |  |  |
Four Tower Bridge [Member] | Conshohocken [Member] | Pennsylvania [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Area of real estate property | ft² |  |  |  | 86,021 |  |  |  |  |
Real estate property debt |  |  |  | $ 9,700,000 |  |  |  |  |
Seven Tower Bridge [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Sale of ownership interest percentage |  |  |  | 20.00% |  |  |  |  |
PJP VII [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Real estate property debt |  |  |  |  | $ 4,200,000 |  | $ 4,200,000 |  |
Guarantees, maximum exposure amount |  |  |  |  | 400,000 |  | 400,000 |  |
4040 Wilson Venture [Member] |  |  |  |  |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Guarantees, maximum exposure amount |  |  |  |  | 41,300,000 |  | 41,300,000 |  |
Construction loan total borrowing capacity |  |  |  |  | $ 150,000,000.0 |  | $ 150,000,000.0 |  |

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- Definition Maturity date of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Paragraph Column C -Subsection 29 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 948 -SubTopic 310 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-29(Column C)) -URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014 + Details
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- Definition For an unclassified balance sheet, the amount due from customers or clients for goods or services that have been delivered or sold in the normal course of business, reduced to their estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(9)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(4)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(5)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition This element represents the carrying value of a short-term real estate loan to finance building costs. The funds are disbursed as needed or in accordance with a prearranged plan; generally, a portion of the funds is disbursed at inception and the remainder as construction progresses. The money is repaid on completion of the project, usually from the proceeds of a mortgage loan. The rate is normally higher than the prime rate, and there is usually an origination fee. The effective yield on these loans tends to be high, and the lender has a security interest in the real property. Note that there are separate concepts for the current and noncurrent portions of long-term construction loans. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(2)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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