Unconsolidated Joint Ventures (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investment [Line Items]
Equity Method Investments	$ 38,181,000	$ 42,018,000
Net sales proceeds received from unconsolidated joint ventures	3,036,000	189,000	0
Fund XIII And REIT Joint Venture [Member]
Investment [Line Items]
Equity Method Investment, Ownership Percentage	72.00%
Equity Method Investments	19,180,000	19,543,000
Fund XII REIT and Joint Venture [Member]
Investment [Line Items]
Equity Method Investment, Ownership Percentage	55.00%
Equity Method Investments	16,329,000	16,688,000
Fund Xl Xll and REIT Joint Venture [Member]
Investment [Line Items]
Equity Method Investment, Ownership Percentage	57.00%
Equity Method Investments	2,672,000	2,871,000
Wells Fremont Associates [Member]
Investment [Line Items]
Equity Method Investment, Ownership Percentage	78.00%
Equity Method Investments	0	2,667,000
Equity Method Investment, Sale Price of Real Estate Sold	3,800,000
Net sales proceeds received from unconsolidated joint ventures	2,700,000
Equity Method Investment, Realized Gain (Loss) on Disposal	71,000
Fund IX, X, XI and REIT Joint Venture [Member]
Investment [Line Items]
Equity Method Investment, Ownership Percentage	4.00%
Equity Method Investments	0	249,000
Equity Method Investment, Sale Price of Real Estate Sold	9,200,000
Net sales proceeds received from unconsolidated joint ventures	300,000
Equity Method Investment, Realized Gain (Loss) on Disposal	$ 45,000