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Organization (Details) ft² in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 ft² Real_Estate_Properties yr shares | Dec. 31, 2016 shares
Real Estate Properties [Line Items] |  |
General and limited partnership interest in the operating partnership (percent) | 89.70% | 89.50%
Restriction on redemption of OP units from date of issuance (years) | yr | 1 |
One OP unit is equivalent to one share of Common Stock (in shares) | shares | 1 |
OP unit conversion rate (in shares) | shares | 1 |
Number Of series Of preferred units outstanding | 1 |
Commercial Real Estate Properties [Member] |  |
Real Estate Properties [Line Items] |  |
Number of real estate properties | 179 |
Net Rentable Area | ft² | 50.3 |
Total Properties Under Construction [ Member] |  |
Real Estate Properties [Line Items] |  |
Number of real estate properties | 12 |
Net Rentable Area | ft² | 6.2 |
Total Office Properties [ Member] |  |
Real Estate Properties [Line Items] |  |
Number of real estate properties | 167 |
Office Properties Under Construction [ Member] |  |
Real Estate Properties [Line Items] |  |
Number of real estate properties | 8 |
Hotel Property [ Member] |  |
Real Estate Properties [Line Items] |  |
Number of real estate properties | 1 |
Retail Properties [ Member] |  |
Real Estate Properties [Line Items] |  |
Number of real estate properties | 5 |
Residential Properties [Member] |  |
Real Estate Properties [Line Items] |  |
Number of real estate properties | 6 |
Residential Properties Under Construction [Member] |  |
Real Estate Properties [Line Items] |  |
Number of real estate properties | 4 |
Series B Cumulative Redeemable Preferred Stock / Unit [Member] |  |
Real Estate Properties [Line Items] |  |
Preferred stock / units, shares / units outstanding (in shares / units) | shares | 80,000 | 80,000
Preferred Stock, Dividend Rate, Percentage | 5.25% |
Depositary shares of Series B Cumulative Redeemable Preferred [Member] |  |
Real Estate Properties [Line Items] |  |
Preferred stock / units, shares / units outstanding (in shares / units) | shares | 8,000,000 |
Series B Preferred Units [Member] |  |
Real Estate Properties [Line Items] |  |
Preferred stock / units, shares / units outstanding (in shares / units) | shares | 80,000 |

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- Definition Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 272 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055 + Details
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