Rental Property - Acquisitions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 building sqft
Acquired during the period
Area (in square feet)	48,500,000
2015 Q1 Acquisitions
Acquired during the period
Area (in square feet)	1,485,717
Number of buildings acquired	5
Purchase price	$ 97,083
Burlington, NJ
Acquired during the period
Area (in square feet)	503,490
Number of buildings acquired	1
Purchase price	34,883
Greenville, SC
Acquired during the period
Area (in square feet)	157,500
Number of buildings acquired	1
Purchase price	4,800
North Haven, CT
Acquired during the period
Area (in square feet)	824,727
Number of buildings acquired	3
Purchase price	$ 57,400