Organization (Details) - Equity Component [Domain] ft² in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015 ft² a shares Vehicles Real_Estate_Properties yr	Dec. 31, 2014 shares
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership (percent)	89.50%	89.50%
Restriction on redemption of OP units from date of issuance (years) | yr	1
in lieu of a cash redemption OP unit to Common Stock conversion (in shares) | shares	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 | shares	1
Number of vehicles in structured parking | Vehicles	43,341
Area of parking (in square feet) | ft²	14.7
Area of undeveloped land parcels owned (in acres) | a	484.4
Commercial Real Estate Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	170
Net Rentable Area (in sf) | ft²	46.3
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	13
Net Rentable Area (in sf) | ft²	4.2
Total Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	162
Class A Office Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	131
Office Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	12
Office Technical Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	31
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
Retail Properties Under Construction [Member]
Real Estate Properties [Line Items]
Number of real estate properties	1
Residential Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	2
Series B Cumulative Redeemable Preferred Stock [Member]
Real Estate Properties [Line Items]
Ratio of depository shares to shares of Series B Preferred Stock	0.01
Series B, Shares Outstanding (in shares) | shares	80,000	80,000
Series B, Dividend Rate, Percentage	5.25%
Depository shares of Series B Cumulative Redeemable Preferred [Member]
Real Estate Properties [Line Items]
Series B, Shares Outstanding (in shares) | shares	8,000,000
Series B Preferred Units [Member]
Real Estate Properties [Line Items]
Series B, Shares Outstanding (in shares) | shares	80,000