Real Estate (Summary of Real Estate Subject to Operating Leases) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property Subject to or Available for Operating Lease [Line Items]
Real estate subject to operating leases, gross	$ 7,038,443	$ 6,596,537
Less accumulated depreciation and amortization	(846,365)	(739,098)
Real estate subject to operating leases before work in process	6,192,078	5,857,439
Accounted for using the operating method, net of accumulated depreciation and amortization	6,241,667	5,881,496
Land and improvements
Property Subject to or Available for Operating Lease [Line Items]
Land and improvements	2,220,519	2,103,185
Buildings and improvements
Property Subject to or Available for Operating Lease [Line Items]
Buildings and improvements	4,812,663	4,488,787
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	$ 49,589	$ 24,057