Real Estate (Summary of Real Estate Subject to Operating Leases) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property Subject to or Available for Operating Lease [Line Items]
Real estate subject to operating leases, gross	$ 7,365,696	$ 7,262,956
Less accumulated depreciation and amortization	(910,559)	(878,236)
Real estate subject to operating leases before work in process	6,455,137	6,384,720
Accounted for using the operating method, net of accumulated depreciation and amortization	6,529,910	6,426,640
Land and improvements
Property Subject to or Available for Operating Lease [Line Items]
Land and improvements	2,305,669	2,288,917
Buildings and improvements
Property Subject to or Available for Operating Lease [Line Items]
Buildings and improvements	5,056,056	4,968,778
Leasehold interests
Property Subject to or Available for Operating Lease [Line Items]
Leasehold interests	3,971	5,261
Work in progress
Property Subject to or Available for Operating Lease [Line Items]
Work in progress for buildings and improvements	74,773	41,920
Asset under Construction
Property Subject to or Available for Operating Lease [Line Items]
Land and improvements	$ 30,434	$ 25,799