Real Estate (Summary of Real Estate Subject to Operating Leases) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property Subject to or Available for Operating Lease [Line Items]
Real estate subject to operating leases, gross	$ 7,267,243	$ 6,593,997
Less accumulated depreciation and amortization	(880,235)	(739,008)
Real estate subject to operating leases before work in process	6,387,008	5,854,989
Work in progress - improvements	41,920	24,057	$ 61,354
Accounted for using the operating method, net of accumulated depreciation and amortization	6,428,928	5,879,046
Revenue recognized	1,411	(12)	$ 153
Balance of accrued rental income	25,916	25,101
Allowances	1,936	3,078
Land and improvements
Property Subject to or Available for Operating Lease [Line Items]
Land and improvements	2,289,749	2,101,923
Buildings and improvements
Property Subject to or Available for Operating Lease [Line Items]
Buildings and improvements	4,972,233	4,487,509
Leasehold interests
Property Subject to or Available for Operating Lease [Line Items]
Leasehold interests	5,261	4,565
Work in progress - improvements
Property Subject to or Available for Operating Lease [Line Items]
Work in progress - improvements	41,920	24,057
Properties under construction
Property Subject to or Available for Operating Lease [Line Items]
Land and improvements	$ 25,799	$ 30,725