Segment Information - Real Estate Assets by Segment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Real estate assets	$ 5,668,775	$ 4,316,307
North America [Member] | Operating Segments [Member] | Lehigh Central PA [Member]
Segment Reporting Information [Line Items]
Real estate assets	877,969	742,464
North America [Member] | Operating Segments [Member] | Chicago Milwaukee [Member]
Segment Reporting Information [Line Items]
Real estate assets	371,149	127,125
North America [Member] | Operating Segments [Member] | Houston [Member]
Segment Reporting Information [Line Items]
Real estate assets	360,779	252,221
North America [Member] | Operating Segments [Member] | Carolinas [Member]
Segment Reporting Information [Line Items]
Real estate assets	245,938	239,052
North America [Member] | Operating Segments [Member] | Industrial Other [Member]
Segment Reporting Information [Line Items]
Real estate assets	964,322	323,200
North America [Member] | Operating Segments [Member] | Minnesota [Member]
Segment Reporting Information [Line Items]
Real estate assets	308,272	333,380
North America [Member] | Operating Segments [Member] | South Florida [Member]
Segment Reporting Information [Line Items]
Real estate assets	358,492	217,769
North America [Member] | Operating Segments [Member] | Richmond Hampton Roads [Member]
Segment Reporting Information [Line Items]
Real estate assets	238,129	231,506
North America [Member] | Operating Segments [Member] | Arizona [Member]
Segment Reporting Information [Line Items]
Real estate assets	348,043	287,895
North America [Member] | Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Real estate assets	369,935	453,931
North America [Member] | Operating Segments [Member] | Philadelphia [Member]
Segment Reporting Information [Line Items]
Real estate assets	229,769	266,144
North America [Member] | Operating Segments [Member] | Southeastern PA [Member]
Segment Reporting Information [Line Items]
Real estate assets	638,211	748,939
North America [Member] | Operating Segments [Member] | Washington DC [Member]
Segment Reporting Information [Line Items]
Real estate assets	170,068	47,820
European Union [Member] | Operating Segments [Member] | United Kingdom [Member]
Segment Reporting Information [Line Items]
Real estate assets	$ 187,699	$ 44,861