Investments in Real Estate and Real Estate Under Construction Summary of development arrangements outstanding (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 sqft
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	1,442,000
Expected Maximum Commitment/Contribution ($ millions)	$ 197.2
Rantoul Illinois [Member] | Industrial Property [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	813,000
Expected Maximum Commitment/Contribution ($ millions)	42.6
Lease Term (Years)	20 years
Capitalization Rate	8.00%	[1]
Bingen, Washington [Member] | Industrial Property [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	124,000
Expected Maximum Commitment/Contribution ($ millions)	18.9
Lease Term (Years)	12 years
Capitalization Rate	10.70%	[1]
Las Vegas, Nevada [Member] | Industrial Property [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	180,000
Expected Maximum Commitment/Contribution ($ millions)	29.6
Lease Term (Years)	20 years
Capitalization Rate	7.30%	[1]
Albany, Georgia [Member] | Retail Property [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	46,000
Expected Maximum Commitment/Contribution ($ millions)	7.5
Lease Term (Years)	15 years
Capitalization Rate	9.00%	[1]
Richmond, Virginia [Member] | Office Property [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	279,000
Expected Maximum Commitment/Contribution ($ millions)	$ 98.6
Lease Term (Years)	15 years
Capitalization Rate	8.00%	[1]

[1] Estimated initial capitalization rate based upon expected maximum commitment/contribution amounts.