Segment Information (Total Assets by Segment) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Assets	$ 6,439,757	$ 5,992,813
Operating Segments [Member]
Segment Reporting Information [Line Items]
Assets	6,368,747	5,889,764
Operating Segments [Member] | Carolinas Richmond [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	543,922	503,920
Operating Segments [Member] | Chicago Minneapolis [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	615,186	616,298
Operating Segments [Member] | Florida [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	533,861	514,431
Operating Segments [Member] | Houston [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	498,584	530,438
Operating Segments [Member] | Lehigh Central PA [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	1,210,746	1,311,815
Operating Segments [Member] | Philadelphia [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	665,843	557,510
Operating Segments [Member] | Southeastern PA [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	241,128	262,155
Operating Segments [Member] | United Kingdom [Member] | United Kingdom [Member]
Segment Reporting Information [Line Items]
Assets	251,824	189,766
Operating Segments [Member] | Other Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Assets	1,807,653	1,403,431
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Assets	$ 71,010	$ 103,049