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Real Estate Investments - Acquisitions (Textual) (Details) $ in Thousands |  |  |  |  |  |  |  | 3 Months Ended | 12 Months Ended |  |
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Jul. 01, 2016 USD ($) a | Jul. 07, 2015 USD ($) a | Jun. 22, 2015 USD ($) ft² a property | May 12, 2015 USD ($) ft² | Apr. 06, 2015 USD ($) a | Apr. 02, 2015 USD ($) ft² | Feb. 19, 2014 USD ($) ft² a property Floor | Dec. 31, 2016 USD ($) a | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) ft² Storey | Sep. 30, 2015 USD ($) | Jun. 30, 2015 USD ($) | Mar. 31, 2015 USD ($) | Dec. 31, 2016 USD ($) a | Dec. 31, 2015 USD ($) ft² Storey | Dec. 31, 2014 USD ($) | Jan. 30, 2017 a | Jun. 30, 2014 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount funded by corporate funds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 20,406 | $ 150,472 | $ 18,443 |  |
Net gain from remeasurement of investments in real estate ventures |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 758 | 458 |  |
Revenue |  |  |  |  |  |  |  | $ 132,086 | $ 129,694 | $ 127,181 | $ 136,502 | $ 153,992 | $ 152,585 | $ 145,648 | $ 150,406 | 525,463 | 602,631 | 596,982 |  |
Net losses |  |  |  |  |  |  |  | (14,058) | $ 6,022 | $ (3,105) | $ 44,091 | (63,941) | $ 18,346 | $ 1,255 | $ 6,710 | 40,191 | (30,401) | 6,975 |  |
Development in Progress |  |  |  |  |  |  |  | $ 297,462 |  |  |  | $ 268,983 |  |  |  | $ 297,462 | 268,983 | 201,360 |  |
Encino Trace - Building I [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Construction in Progress, Gross |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 38,800 |  |
2100 Market Street [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acreage of land | a |  | 0.8 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Land |  | $ 18,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount funded by corporate funds |  | 16,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount Deferred |  | $ 2,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement Period |  | 24 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
25 M Street [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acreage of land | a |  |  |  |  | 0.8 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Land |  |  |  |  | $ 20,300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition Costs |  |  |  |  | $ 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of Real Estate Property | ft² |  |  |  | 271,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
25 M Street [Member] | Brandywine 25 M Street [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percent of Acquired Entity |  |  |  | 95.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Garza Land Sale [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of land under agreement to sell | a |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.7 |
Garza Land Acquisition [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acreage of land | a | 34.6 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross purchase value of assets | $ 20,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition costs | 1,900 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount funded by corporate funds | $ 20,400 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of land under agreement to sell | a |  |  |  |  |  |  |  | 9.5 |  |  |  |  |  |  |  | 9.5 |  |  |  |
Broadmoor Austin Associates [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acreage of land | a |  |  | 66.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Land |  |  | $ 143,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount funded by corporate funds |  |  | $ 81,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of ownership interests |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Property units | property |  |  | 7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase Price of Assets |  |  | $ 211,400 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Carrying amount of Investment |  |  | $ 66,300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  | 1,112,236 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lease percentage of acquired property |  |  | 100.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Funds Held in Escrow |  |  | $ 62,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mortgage Debt Paid at Closing |  |  | 51,200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition Costs |  |  | $ 200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 200 |  |
Ownership percentage |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net gain from remeasurement of investments in real estate ventures |  |  | $ 800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 26,400 | 13,200 |  |  |
Net losses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5,200 | $ 7,200 |  |  |
Building, land and improvements |  |  | $ 163,271 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
25 M Street [Member] | 25 M Street [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Land |  |  |  | $ 1,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Asset Acquisition Ownership Percent |  |  |  | 5.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
618 Market Street [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Land |  |  |  |  |  | $ 19,400 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of Real Estate Property | ft² |  |  |  |  |  | 14,404 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Parking Spaces | ft² |  |  |  |  |  | 330 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value of Contingent Consideration |  |  |  |  |  | $ 1,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration, Cash |  |  |  |  |  | 17,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Building, land and improvements |  |  |  |  |  | 19,200 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible Assets |  |  |  |  |  | $ 200 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Encino Trace - Land [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acreage of land | a |  |  |  |  |  |  | 54.1 |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Land |  |  |  |  |  |  | $ 14,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Rentable Square Feet | ft² |  |  |  |  |  |  | 320,000 |  |  |  |  | 320,000 |  |  |  |  | 320,000 |  |  |
Lease percentage of acquired property |  |  |  |  |  |  | 75.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Funds Held in Escrow |  |  |  |  |  |  | $ 1,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Construction in Progress, Gross |  |  |  |  |  |  | 8,400 |  |  |  |  |  |  |  |  |  |  |  |  |
Development in Progress |  |  |  |  |  |  | $ 4,600 |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,600
Number of potential development properties | property |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of floors of a building |  |  |  |  |  |  | 4 |  |  |  |  | 4 |  |  |  |  | 4 |  |  |

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- Definition Payments to acquire real estate gross. + References No definition available. + Details
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- Definition Area of land held. + References No definition available. + Details
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- Definition Amount of direct costs of the business combination including legal, accounting, and other costs incurred to consummate the business acquisition. + References No definition available. + Details
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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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- Definition Percentage of voting equity interests acquired at the acquisition date in the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463 + Details
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- Definition Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477 + Details
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- Definition Amount of intangible assets, excluding goodwill, acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=73530397&loc=d3e4845-128472 + Details
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- Definition The amount of property, plant, and equipment recognized as of the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=73530397&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=73531372&loc=d3e2207-128464 + Details
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- Definition Fair value at acquisition-date of the equity interest in the acquiree held by the acquirer, immediately before the acquisition date for businesses combined in stages. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463 + Details
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- Definition Percentage of voting equity interests acquired in a business combination achieved in stages, including equity interests in the acquiree held by the acquirer immediately before the acquisition date and acquired at the acquisition date. + References No definition available. + Details
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- Definition In a business combination achieved in stages, this element represents the amount of gain recognized by the entity as a result of remeasuring to fair value the equity interest in the acquiree it held before the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g)(2) -URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463 + Details
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- Definition Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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- Definition The current amount of expenditures for a real estate project that has not yet been completed. + 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 210.7-03.10) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Phase -URI http://asc.fasb.org/extlink&oid=49177889 + Details
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571 + Details
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- Definition The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.10) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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