Crude Oil Supply and Inventory Purchase Agreement - Payable (Receivable) Under Supply and Offtake Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Oil and Gas, Delivery Commitment [Line Items]
Revolving over/short inventory financing liability	$ 102.8	$ 207.0
Total Obligations Under Supply and Offtake Agreements	323.2	477.3
Less: Current portion	102.8	332.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	220.4	144.8
Other current payable for monthly activity true-up	13.6	(23.0)
El Dorado Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability		125.5
Revolving over/short inventory financing liability	80.6	93.0
Total Obligations Under Supply and Offtake Agreements	181.1	218.5
Less: Current portion	80.6	218.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	100.5	0.0
Other current payable for monthly activity true-up	12.6	(16.4)
Big Spring refinery
Oil and Gas, Delivery Commitment [Line Items]
Revolving over/short inventory financing liability	19.7	73.5
Total Obligations Under Supply and Offtake Agreements	68.8	130.7
Less: Current portion	19.7	73.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	49.1	57.2
Other current payable for monthly activity true-up	1.0	(3.1)
Krotz Spring Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability		87.6
Revolving over/short inventory financing liability	2.5	40.5
Total Obligations Under Supply and Offtake Agreements	73.3	128.1
Less: Current portion	2.5	40.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	70.8	87.6
Other current payable for monthly activity true-up	0.0	(3.5)
Baseline Step-Out Liability
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	220.4	270.3
Baseline Step-Out Liability | El Dorado Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	100.5
Baseline Step-Out Liability | Big Spring refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	49.1	$ 57.2
Baseline Step-Out Liability | Krotz Spring Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	$ 70.8