Notes Payable (Details) (USD $)				9 Months Ended		1 Months Ended
	Sep. 30, 2012 property	Dec. 31, 2011	Sep. 30, 2012 Epic Center, One Brittany, Two Brittany, Tice Building and One Edgewater Plaza properties	Sep. 30, 2012 Notes payable	Dec. 31, 2011 Notes payable	Oct. 31, 2012 Secured loan Defaulted item property	Aug. 31, 2012 Secured loan Defaulted item	Sep. 30, 2012 Secured loan Defaulted property	Sep. 30, 2012 Secured loan Defaulted Maximum	Sep. 30, 2012 Secured loan Defaulted Minimum	Sep. 30, 2012 Secured loan Defaulted 17655 Waterview, Ashford Perimeter and Riverview Tower properties	Sep. 30, 2012 Secured loan Imminent default property
Long-term debt
Debt bearing interest at annual variable rate				$ 368,300,000
Variable rate debt effectively fixed or capped through the use of interest rate hedges				310,000,000
Stated annual interest rate, low end of range (as a percent)				3.23%
Stated annual interest rate, high end of range (as a percent)				9.80%
Effective weighted average interest rate excluding loans in default (as a percent)				5.53%
Basis points incurred above stated interest rate in event of default (as a percent)									5.00%	4.00%
Overall effective weighted average interest rate (as a percent)				5.77%
Number of non-recourse property loans								6
Number of properties secured	52							9				1
Number of properties to which a receiver is appointed						1	1
Principal payments due in:
October - December 2012				5,799,000
2013				227,670,000
2014				264,633,000
2015				503,839,000
2016				950,065,000
Thereafter				221,762,000
unamortized discount				(19,000)
Total	2,173,749,000	2,367,401,000		2,173,749,000	2,400,000,000			158,800,000			93,400,000	82,600,000
Increase in principal payments in 2012											93,100,000
Decrease in principal payments in 2013											500,000
Decrease in principal payments in 2014											500,000
Decrease in principal payments in 2015											32,400,000
Decrease in principal payments in 2016											59,700,000
Amount of demand for immediate payment of secured non-recourse loans			$ 49,000,000