Investments in Real Estate and Real Estate Under Construction Summary of development arrangements outstanding (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 sqft
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	1,247,000
Expected Maximum Commitment/Contribution ($ millions)	$ 313.3
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
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
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
Lake Jackson, Texas [Member] | Office and R and D Property [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	664,000
Expected Maximum Commitment/Contribution ($ millions)	$ 166.2
Lease Term (Years)	20 years