Organization (Details) (USD $)	9 Months Ended												60 Months Ended			3 Months Ended		3 Months Ended
	Sep. 30, 2013 Y sqft Vehicles acre	Sep. 30, 2012	Sep. 30, 2013 Commercial Real Estate Properties [Member] Real_Estate_Properties sqft	Sep. 30, 2013 Total Properties Under Construction [Member] Real_Estate_Properties sqft	Sep. 30, 2013 Total Office Properties [Member] Real_Estate_Properties	Sep. 30, 2013 Class A Office Properties [Member] Real_Estate_Properties	Sep. 30, 2013 Office Properties Under Construction [Member] Real_Estate_Properties	Sep. 30, 2013 Office/Technical Properties [Member] Real_Estate_Properties	Sep. 30, 2013 Hotel Properties [Member] Real_Estate_Properties	Sep. 30, 2013 Retail Properties [Member] Real_Estate_Properties	Sep. 30, 2013 Residential Properties [Member] Real_Estate_Properties	Sep. 30, 2013 Residential Properties Under Construction [Member] Real_Estate_Properties	Mar. 26, 2018 Series B Cumulative Redeemable Preferred Stock [Member]	Sep. 30, 2013 Series B Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series B Cumulative Redeemable Preferred Stock [Member]	Sep. 30, 2013 Series Two Preferred Units [Member]	Sep. 30, 2013 Series B Preferred Units [Member]	Sep. 30, 2013 series four preferred units [Member]	Aug. 07, 2013 series four preferred units [Member]
Real Estate Properties [Line Items]
General and limited partnership interest in the operating partnership (percent)	89.20%	88.60%
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
Series B, Units Outstanding														80,000	0		80,000
Ratio of depository shares to shares of Series B Preferred Stock														0.01
Series B, Dividend Rate, Percentage													5.25%
Preferred Units Liquidation Preference																$ 50.00		$ 50.00	$ 50.00
Number of series of preferred units outstanding	3
OP Units for each Preferred Unit (in shares)																1.312336
Number of real estate properties			177	8	169	130	7	39	1	4	3	1
Net Rentable Area			44,600,000	2,800,000
Number of vehicles in structured parking	46,221
Area of parking structures (in square feet)	15,700,000
Area of undeveloped land parcels owned (in acres)	512.6
Preferred Stock Dividend Payable Per Share																		$ 0.25
Series Four Preferred Units Annual Dividend Payable Rate																		2.00%