Segment Information - Total Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Assets	$ 6,819,075	$ 6,439,757
Operating Segments [Member]
Segment Reporting Information [Line Items]
Assets	6,680,128	6,368,747
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Assets	138,947	71,010
North America [Member] | Operating Segments [Member] | Carolinas Richmond [Member]
Segment Reporting Information [Line Items]
Assets	524,967	543,922
North America [Member] | Operating Segments [Member] | Chicago Minneapolis [Member]
Segment Reporting Information [Line Items]
Assets	600,838	615,186
North America [Member] | Operating Segments [Member] | Florida [Member]
Segment Reporting Information [Line Items]
Assets	546,526	533,861
North America [Member] | Operating Segments [Member] | Houston [Member]
Segment Reporting Information [Line Items]
Assets	537,500	498,584
North America [Member] | Operating Segments [Member] | Lehigh Central PA [Member]
Segment Reporting Information [Line Items]
Assets	1,220,160	1,210,746
North America [Member] | Operating Segments [Member] | Philadelphia [Member]
Segment Reporting Information [Line Items]
Assets	640,790	665,843
North America [Member] | Operating Segments [Member] | Southeastern PA [Member]
Segment Reporting Information [Line Items]
Assets	145,778	241,128
North America [Member] | Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Assets	2,063,248	1,807,653
UNITED KINGDOM | Operating Segments [Member] | United Kingdom [Member]
Segment Reporting Information [Line Items]
Assets	$ 400,321	$ 251,824