Organization (Details)	3 Months Ended
	Mar. 31, 2012 Y sqft acre	Mar. 31, 2011
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership	88.40%	87.10%
Restriction on redemption of OP units from date of issuance (years)	1
One OP unit is equivalent to one share of Common Stock	1
Number of series of preferred units outstanding	1
OP unit conversion rate	1
Number of vehicles in structured parking	44,703
Area of parking in square feet	15,200,000
Area of undeveloped land parcels owned in acres	510.5
Value-added fund institutional investors	2
Commercial Real Estate Properties [Member]
Real Estate Properties [Line Items]
Square footage of real estate property	43,300,000
Number of real estate properties	153
Total Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	146
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Square footage of real estate property	2,800,000
Number of real estate properties	8
Office Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	7
Class A Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	127
Office/Technical Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	19
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	3
Residential Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	3
Residential Properties Under Construction [Member]
Real Estate Properties [Line Items]
Number of real estate properties	1
Investments Through Value-Added Fund [Member]
Real Estate Properties [Line Items]
Number of real estate properties	24