Indebtedness (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 IndustrialProperty sqft
Mortgage loans obtained
Loan Principal	$ 280,317
Property Carrying Value	319,685
Mortgage Financing I - VIII [Member]
Mortgage loans obtained
Loan Principal	178,300
Interest Rate	4.45%
Origination/Assumption Date	May 02, 2011
Maturity Date	Jun. 01, 2018
Amortization Period	30 years
Number of Industrial Properties Collateralizing Mortgage	32
Gross Leaseable Area	5,900,000
Property Carrying Value	206,291
Mortgage Financing IX [Member]
Mortgage loans obtained
Loan Principal	24,417
Interest Rate	5.579%
Origination/Assumption Date	May 26, 2011
Maturity Date	Feb. 01, 2016
Amortization Period	30 years
Number of Industrial Properties Collateralizing Mortgage	1
Gross Leaseable Area	700,000
Property Carrying Value	28,991
Mortgage Financing X [Member]
Mortgage loans obtained
Loan Principal	77,600
Interest Rate	4.85%
Origination/Assumption Date	Sep. 23, 2011
Maturity Date	Oct. 01, 2021
Amortization Period	30 years
Number of Industrial Properties Collateralizing Mortgage	24
Gross Leaseable Area	2,300,000
Property Carrying Value	$ 84,403