Debt Covenant Ratios (Details)	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Debt Instrument Covenant Line Of Credit And Term Leverage Ratio, Maximum	6.5	5.4
Debt Instrument Covenant, Cash Dividend, Maximum Of Funds From Operations, Percentage	95.00%
Dividend Limitation Leverage Condition, Leverage Ratio Trigger	6.0
Credit Agreement
Debt Instrument [Line Items]
Net total lease adjusted leverage ratio	5.5	5.7
Net secured debt lease adjusted leverage ratio	2.3	2.7
Bond leverage ratio, per indentures	5.9	5.2
Fixed charge coverage ratio	2.2	2.4
Credit Agreement | Maximum
Debt Instrument [Line Items]
Net total lease adjusted leverage ratio	6.5
Net secured debt lease adjusted leverage ratio	4.0
Bond leverage ratio, per indentures	6.5
Credit Agreement | Minimum
Debt Instrument [Line Items]
Fixed charge coverage ratio	1.5