Debt - Covenant Ratios (Details) $ in Thousands	Sep. 30, 2019 USD ($)	Dec. 31, 2018
Credit Agreement
Debt Instrument [Line Items]
Letters of credit outstanding	$ 35,241
Net total lease adjusted leverage ratio	5.8	5.6
Net secured debt lease adjusted leverage ratio	2.3	2.6
Bond leverage ratio (not lease adjusted)	6.1	5.8
Fixed charge coverage ratio	2.1	2.2
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 (not lease adjusted)	7.0
Credit Agreement | Minimum
Debt Instrument [Line Items]
Bond leverage ratio (not lease adjusted)	6.5
Fixed charge coverage ratio	1.5
Revolving Credit Facility
Debt Instrument [Line Items]
Letters of credit outstanding	$ 16,843
Senior Notes | Maximum
Debt Instrument [Line Items]
Bond leverage ratio (not lease adjusted)	6.5
Senior Notes 4.875 Percent due 2029, Senior Notes 4.875 Percent due 2027, GBP Notes due 2025 and 5.25 Percent Notes
Debt Instrument [Line Items]
Debt instrument covenant, indenture, leverage ratio maximum	7.0