Organization (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 Y sqft Vehicles acre Investors	Dec. 31, 2011
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership (percent)	89.00%	88.30%
Restriction on redemption of OP units from date of issuance (years)	1
One OP unit is equivalent to one share of Common Stock (in shares)	1
OP unit conversion rate (in shares)	1
Number Of series Of preferred units outstanding	2
Number of vehicles in structured parking	46,833
Area of parking (in square feet)	15,900,000
Area of undeveloped land parcels owned (in acres)	509.3
Value-added fund institutional investors (number of investors)	2
Commercial Real Estate Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	157
Net Rentable Area	44,400,000
Total Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	9
Net Rentable Area	2,800,000
Total Office Properties [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	149
Class A Office Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	132
Office Properties Under Construction [ Member]
Real Estate Properties [Line Items]
Number of real estate properties	8
Office Technical Properties [Member]
Real Estate Properties [Line Items]
Number of real estate properties	17
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	4
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	23
Office Complexes	2
Series Two Preferred Units [Member]
Real Estate Properties [Line Items]
OP Units for each Preferred Unit (in shares)	1.312336
Preferred Units Liquidation Preference	50.00
series four preferred units [Member]
Real Estate Properties [Line Items]
Preferred Units Liquidation Preference	50.00
Quarterly Distributions to Series Four Preferred Units	0.25
Series Four Preferred Units Annual Dividend Payable Rate	2.00%