Real Estate Properties Sold (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 sqft properties	Dec. 31, 2012 properties sqft
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold	58	50
Sold Real Estate Property, Square Feet	5,123,172	3,038,057
Gross proceeds from sale of operating properties	$ 491,780	$ 228,460
Lehigh Central PA [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold	1	1
Sold Real Estate Property, Square Feet	101,750	45,000
Gross proceeds from sale of operating properties	8,650	2,025
Chicago Milwaukee [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold		20
Sold Real Estate Property, Square Feet		996,115
Gross proceeds from sale of operating properties		69,861
Carolinas [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold	1	13
Sold Real Estate Property, Square Feet	59,200	704,120
Gross proceeds from sale of operating properties	2,000	55,228
Industrial Other [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold	2	8
Sold Real Estate Property, Square Feet	80,635	632,758
Gross proceeds from sale of operating properties	4,422	49,386
Minnesota [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold	12
Sold Real Estate Property, Square Feet	915,693
Gross proceeds from sale of operating properties	71,493
South Florida [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold		1
Sold Real Estate Property, Square Feet		47,442
Gross proceeds from sale of operating properties		4,143
Richmond Hampton Roads [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold	1	3
Sold Real Estate Property, Square Feet	86,170	289,278
Gross proceeds from sale of operating properties	10,978	22,131
Other Segments [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold	34	1
Sold Real Estate Property, Square Feet	2,226,500	15,000
Gross proceeds from sale of operating properties	187,853	2,386
Philadelphia [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold	2
Sold Real Estate Property, Square Feet	656,350
Gross proceeds from sale of operating properties	103,650
Southeastern PA [Member] | Operating Segments [Member]
Disposition Disclosures [Line Items]
Number of Real Estate Properties Sold	5	3
Sold Real Estate Property, Square Feet	996,874	308,344
Gross proceeds from sale of operating properties	$ 102,734	$ 23,300