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Investments in Unconsolidated Joint Ventures Narrative (Details) $ in Thousands | Jan. 24, 2019 USD ($) ft² | Mar. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
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Schedule of Equity Method Investments [Line Items] |  |  |
Mortgage notes payable, net |  | $ 2,959,908 | $ 2,964,572
Annapolis Junction Building Six [Member] |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Ownership Percentage | 50.00% |  |
Mortgage notes payable, net | $ 13,000 |  |
Debt Instrument, Basis Spread on Variable Rate | 2.00% |  |
Number of extensions | 1 |  |
Extension Option (in years) | 1 |  |
Debt instrument, borrowing capacity | $ 14,300 |  |
Net Rentable Area (in sf) | ft² | 119,000 |  |

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- Definition Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower. + References Reference 1: 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(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: 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(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 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(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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