Combined Guarantor Subsidiary - Contingencies - Narrative (Details)	3 Months Ended
	Mar. 31, 2019 USD ($)
Condensed Financial Statements, Captions [Line Items]
Environmental liability insurance, maximum coverage per incident (up to)	$ 10,000,000
Environmental liability insurance, annual coverage limit (up to)	50,000,000
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Environmental liability insurance, maximum coverage per incident (up to)	10,000,000
Environmental liability insurance, annual coverage limit (up to)	$ 50,000,000