Debt Covenant Ratios (Details) - Credit Agreement	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Net total lease adjusted leverage ratio	5.8	5.7
Net secured debt lease adjusted leverage ratio	2.5	2.7
Bond leverage ratio, per indentures	5.6	5.2
Fixed charge coverage ratio	2.2	2.4
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
Minimum
Debt Instrument [Line Items]
Fixed charge coverage ratio	1.5