Segment Information - Total Assets by Segment (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Assets	$ 6,775,560,000	$ 5,174,179,000
Operating Segments [Member] | Lehigh Central PA [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	938,824,000	779,929,000
Operating Segments [Member] | Chicago Milwaukee [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	413,585,000	153,128,000
Operating Segments [Member] | Houston [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	380,248,000	266,061,000
Operating Segments [Member] | Carolinas [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	257,230,000	249,479,000
Operating Segments [Member] | Industrial Other [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	1,315,732,000	639,629,000
Operating Segments [Member] | Minnesota [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	335,613,000	353,428,000
Operating Segments [Member] | South Florida [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	380,138,000	227,754,000
Operating Segments [Member] | Richmond Hampton Roads [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	250,008,000	250,600,000
Operating Segments [Member] | Arizona [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	364,231,000	300,149,000
Operating Segments [Member] | United Kingdom [Member] | European Union [Member]
Segment Reporting Information [Line Items]
Assets	247,537,000	72,323,000
Operating Segments [Member] | Other Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	465,997,000	554,352,000
Operating Segments [Member] | Philadelphia [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	316,810,000	348,541,000
Operating Segments [Member] | Southeastern PA [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	695,966,000	814,460,000
Operating Segments [Member] | Washington DC [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	180,621,000	50,575,000
Corporate, Non-Segment [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	$ 233,020,000	$ 113,771,000