Real Estate (Summary of Real Estate Subject to Operating Leases) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Property Subject to or Available for Operating Lease [Line Items]
Real estate subject to operating leases, gross	$ 6,681,303	$ 6,589,961
Less accumulated depreciation and amortization	(773,659)	(738,530)
Real estate subject to operating leases before work in process	5,907,644	5,851,431
Accounted for using the operating method, net of accumulated depreciation and amortization	5,944,220	5,875,488
Land and improvements
Property Subject to or Available for Operating Lease [Line Items]
Land and improvements	2,123,019	2,100,367
Buildings and improvements
Property Subject to or Available for Operating Lease [Line Items]
Buildings and improvements	4,553,023	4,485,029
Leasehold interests
Property Subject to or Available for Operating Lease [Line Items]
Leasehold interests	5,261	4,565
Work in progress
Property Subject to or Available for Operating Lease [Line Items]
Work in progress	$ 36,576	$ 24,057