Investments in Real Estate and Real Estate Under Construction (Details) (USD $)	3 Months Ended
	Mar. 31, 2013 sqft	Mar. 31, 2012	Dec. 31, 2012
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial Cost Basis	$ 123,272,000
Land	15,055,000
Building and Improvements	99,821,000
Lease in-place Value	8,396,000
Aggregate aquisition expenses	193,000	3,000
Square Feet	1,146,000
Expected Maximum Commitment/Contribution	111,200,000
Development in Process	47,041,000		65,122,000
Development Deals [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Real Estate Investment Capitalized Interest	833,000	435,000
Long Island City New York [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Real Estate Investments, Invested Capital Threshold for Distribution	25,000,000
Office Property [Member] | Denver Colorado [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	167,000
Expected Maximum Commitment/Contribution	39,000,000
Lease Term (Years)	15
Office Property [Member] | Bingen, Washington [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	124,000
Expected Maximum Commitment/Contribution	20,800,000
Industrial Property [Member] | Long Island City New York [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial Cost Basis	41,872,000
Land	0
Building and Improvements	41,872,000
Lease in-place Value	0
Industrial Property [Member] | Houston, Texas [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial Cost Basis	81,400,000
Land	15,055,000
Building and Improvements	57,949,000
Lease in-place Value	8,396,000
Industrial Property [Member] | Rantoul Illinois [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	813,000
Expected Maximum Commitment/Contribution	42,600,000
Lease Term (Years)	20
Retail Property [Member] | Tuscaloosa Alabama [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	42,000
Expected Maximum Commitment/Contribution	8,800,000
Lease Term (Years)	15
Minimum [Member] | Industrial Property [Member] | Bingen, Washington [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Lease Term (Years)	10
Maximum [Member] | Industrial Property [Member] | Bingen, Washington [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Lease Term (Years)	20
Up to $25,000 [Member] | Long Island City New York [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Real Estate Investments, Distribution Percentage	6.30%
Up to $25,000 [Member] | Maximum [Member] | Long Island City New York [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Real Estate Investments, Invested Capital Threshold for Distribution	25,000,000
In excess of $25,000 [Member] | Long Island City New York [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Real Estate Investments, Distribution Percentage	11.00%
In excess of $25,000 [Member] | Minimum [Member] | Long Island City New York [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Real Estate Investments, Invested Capital Threshold for Distribution	25,000,000
Any Excess Return [Member] | Long Island City New York [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Real Estate Investments, Distribution Percentage	50.00%
Omaha, Nebraska Acquistion [Member] | Office Property [Member] | Omaha, Nebraska [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Lease Term (Years)	20
Business acquisition, cash paid	$ 39,125,000