Schedule III - Schedule of Real Estate and Accumulated Depreciation (Schedule of Real Estate and Accumulated Depreciation, by Property) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) site	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Description | site	27,909
Encumbrances	$ 6,805,000
Gross Amount Carried at Close of Current Period	5,340,858	$ 5,079,660	$ 4,839,874	$ 4,577,296
Accumulated Depreciation at Close of Current Period	$ (2,627,841)	$ (2,396,587)	$ (2,160,530)	$ (1,912,906)
Date of Construction	Various
Date Acquired	Various
Secured debt	$ 6,800,000
Maximum [Member]
Life on Which Depreciation in Latest Income Statement is Computed	20 years
Minimum [Member] | Real Estate, Gross [Member]
Concentration risk percentage of revenue	5.00%