Capital and Financing Transactions (Details) (USD $)	6 Months Ended					6 Months Ended				7 Months Ended			6 Months Ended					6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Feb. 10, 2012 111 East Wacker [Member]	Jan. 09, 2012 111 East Wacker [Member]	Jun. 30, 2012 Hayden Ferry Lakeside II [Member] sqft	Feb. 10, 2012 Hayden Ferry Lakeside II [Member] sqft	Mar. 09, 2012 Bank of America Plaza [Member] sqft	May 31, 2012 The Pinnacle at Jackson Place [Member]	Jul. 31, 2012 Fund I Assets [Member]	Jun. 30, 2012 Mortgages [Member]	Jun. 30, 2012 Mortgages [Member] Liabilities related to assets held for sale [Member]	Jun. 30, 2012 Mortgages [Member] The Pointe [Member]	Feb. 10, 2012 Mortgages [Member] The Pointe [Member]	Jan. 11, 2012 Mortgages [Member] The Pointe [Member]	Feb. 10, 2012 Minimum [Member] Hayden Ferry Lakeside II [Member]	Feb. 10, 2012 Maximum [Member] Hayden Ferry Lakeside II [Member]	Jun. 30, 2012 New Facilities [Member]	Jun. 30, 2012 New Facilities [Member] Minimum [Member]	Jun. 30, 2012 New Facilities [Member] Maximum [Member]	Jun. 30, 2012 Senior Unsecured Revolving Credit Facility [Member]	Jun. 30, 2012 Working Capital Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Number of banks in the consortium																		8
Maximum borrowing capacity																		$ 200,000,000			$ 190,000,000	$ 10,000,000
Expiration date prior to modification																		Jan. 31, 2014
Expiration date subsequent to modification																		Mar. 29, 2016
Optional period to extend term of facility																		1 year 0 months 0 days
Size of the accordion feature																			50,000,000	160,000,000
Variable rate basis	LIBOR					LIBOR
Basis spread on variable rate (in hundredths)																250.00%	350.00%		160.00%	235.00%
Commitment fee (in hundredths)																			25.00%	35.00%
Amount outstanding under credit facilities																		111,300,000
Debt Instrument [Line Items]
Mortgage notes payable	551,564,000		498,012,000				50,000,000	16,300,000	29,500,000		581,200,000				23,500,000
Liabilities related to assets held for sale												29,600,000
Weighted average interest rate (in hundredths)											5.50%
Interest rate on mortgage (in hundredths)					6.30%			7.10%	5.20%						4.00%
Gross Sales Price					150,600,000				29,500,000
Debt assumed by buyer on sale of real estate					147,900,000					76,700,000
Maturity Date of Debt				July 2016			July 2018	May 2012						February 2019
Interest only period of mortgage (in months)													0 years 42 months 0 days
Proportionate share of mortgage loan							15,000,000			19,200,000
Area of real estate property (in square feet)						300,000	300,000	337,000
Variable rate basis	LIBOR					LIBOR
Basis spread on variable rate (in hundredths)																250.00%	350.00%		160.00%	235.00%
Repayments of non-recourse mortgage loan	$ 20,256,000	$ 101,233,000
Number of Fund assets sold										4