Investments in Real Estate and Real Estate Under Construction - Summary of development arrangements outstanding (Details) ft² in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) ft²
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	2,319
Expected Maximum Commitment/Contribution | $	$ 346,313
Richmond, Virginia [Member] | Office Building [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	330
Expected Maximum Commitment/Contribution | $	$ 110,137
Lease Term (Years)	15 years
Anderson, South Carolina [Member] | Industrial property [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	1,325
Expected Maximum Commitment/Contribution | $	$ 70,012
Lease Term (Years)	20 years
Lake Jackson, Texas [Member] | Office Building [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Square Feet	664
Expected Maximum Commitment/Contribution | $	$ 166,164
Lease Term (Years)	20 years