Crude Oil Supply and Inventory Purchase Agreement - Payable (Receivable) Under Supply and Offtake Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Oil and Gas Delivery Commitments and Contracts [Line Items]
Revolving over/short product financing liability	$ 140.9	$ 46.9
Revolving Step-Out Liability (prior to January 2019 amendments)		265.7
Total Obligations Under Supply and Offtake Agreements	408.6	362.2
Less: Current portion	265.0	312.6
Obligations Under Supply and Offtake Agreements - Noncurrent portion	143.6	49.6
Other receivable for monthly activity true-up (included in current receivables)	(12.4)	(6.8)
El Dorado Refinery
Oil and Gas Delivery Commitments and Contracts [Line Items]
Revolving over/short product financing liability	80.4	0.0
Revolving Step-Out Liability (prior to January 2019 amendments)		152.6
Total Obligations Under Supply and Offtake Agreements	204.5	152.6
Less: Current portion	204.5	152.6
Obligations Under Supply and Offtake Agreements - Noncurrent portion	0.0	0.0
Other receivable for monthly activity true-up (included in current receivables)	(6.9)	(7.8)
Big Spring refinery
Oil and Gas Delivery Commitments and Contracts [Line Items]
Revolving over/short product financing liability	32.8	46.9
Revolving Step-Out Liability (prior to January 2019 amendments)		0.0
Total Obligations Under Supply and Offtake Agreements	89.3	96.5
Less: Current portion	32.8	46.9
Obligations Under Supply and Offtake Agreements - Noncurrent portion	56.5	49.6
Other receivable for monthly activity true-up (included in current receivables)	(2.4)	(0.4)
Krotz Spring Refinery
Oil and Gas Delivery Commitments and Contracts [Line Items]
Revolving over/short product financing liability	27.7	0.0
Revolving Step-Out Liability (prior to January 2019 amendments)		113.1
Total Obligations Under Supply and Offtake Agreements	114.8	113.1
Less: Current portion	27.7	113.1
Obligations Under Supply and Offtake Agreements - Noncurrent portion	87.1	0.0
Other receivable for monthly activity true-up (included in current receivables)	(3.1)	1.4
Baseline Step-Out Liability
Oil and Gas Delivery Commitments and Contracts [Line Items]
Baseline Step-Out Liability	267.7	49.6
Baseline Step-Out Liability | El Dorado Refinery
Oil and Gas Delivery Commitments and Contracts [Line Items]
Baseline Step-Out Liability	124.1	0.0
Baseline Step-Out Liability | Big Spring refinery
Oil and Gas Delivery Commitments and Contracts [Line Items]
Baseline Step-Out Liability	56.5	49.6
Baseline Step-Out Liability | Krotz Spring Refinery
Oil and Gas Delivery Commitments and Contracts [Line Items]
Baseline Step-Out Liability	$ 87.1	$ 0.0