Segment Information - Total Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Assets	$ 6,159,635	$ 5,992,813
Operating Segments [Member]
Segment Reporting Information [Line Items]
Assets	6,107,158	5,889,764
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Assets	52,477	103,049
North America [Member] | Operating Segments [Member] | Carolinas Richmond [Member]
Segment Reporting Information [Line Items]
Assets	512,329	503,920
North America [Member] | Operating Segments [Member] | Chicago Minneapolis [Member]
Segment Reporting Information [Line Items]
Assets	609,962	616,298
North America [Member] | Operating Segments [Member] | Florida [Member]
Segment Reporting Information [Line Items]
Assets	507,873	514,431
North America [Member] | Operating Segments [Member] | Houston [Member]
Segment Reporting Information [Line Items]
Assets	529,946	530,438
North America [Member] | Operating Segments [Member] | Lehigh Central PA [Member]
Segment Reporting Information [Line Items]
Assets	1,350,454	1,311,815
North America [Member] | Operating Segments [Member] | Philadelphia [Member]
Segment Reporting Information [Line Items]
Assets	610,025	557,510
North America [Member] | Operating Segments [Member] | Southeastern PA [Member]
Segment Reporting Information [Line Items]
Assets	271,035	262,155
North America [Member] | Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Assets	1,487,741	1,403,431
UNITED KINGDOM | Operating Segments [Member] | United Kingdom [Member]
Segment Reporting Information [Line Items]
Assets	$ 227,793	$ 189,766