Real Estate (Summary of Real Estate Subject to Operating Leases) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Property Subject to or Available for Operating Lease [Line Items]
Real estate subject to operating leases, gross	$ 5,969,278	$ 5,815,108
Less accumulated depreciation and amortization	(650,377)	(620,188)
Real estate subject to operating leases before work in process	5,318,901	5,194,920
Accounted for using the operating method, net of accumulated depreciation and amortization	5,343,433	5,256,274
Land and improvements
Property Subject to or Available for Operating Lease [Line Items]
Land and improvements	1,944,175	1,922,579
Buildings and improvements
Property Subject to or Available for Operating Lease [Line Items]
Buildings and improvements	4,020,538	3,891,239
Leasehold interests
Property Subject to or Available for Operating Lease [Line Items]
Leasehold interests	4,565	1,290
Work in progress
Property Subject to or Available for Operating Lease [Line Items]
Work in progress	$ 24,532	$ 61,354