Organization (Details) ft² in Millions	12 Months Ended
	Dec. 31, 2018 ft² Real_Estate_Properties yr shares	Dec. 31, 2017 shares
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership (percent)	89.70%	89.70%
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	197
Net Rentable Area | ft²	51.6
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	11
Net Rentable Area | ft²	5.3
Total Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	178
Office Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	9
Retail Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	12
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	2
Hotel Property [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	1
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