Crude Oil Supply and Inventory Purchase Agreement - Payable (Receivable) Under Supply and Offtake Agreements (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Oil and Gas, Delivery Commitment [Line Items]
Revolving over/short inventory financing liability	$ 99.0	$ 207.0
Total Obligations Under Supply and Offtake Agreements	314.0	477.3
Less: Current portion	99.0	332.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	215.0	144.8
Other current payable (receivable) for monthly activity true-up	5.6	(23.0)
El Dorado Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability		125.5
Revolving over/short inventory financing liability	63.6	93.0
Total Obligations Under Supply and Offtake Agreements	161.5	218.5
Less: Current portion	63.6	218.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	97.9	0.0
Other current payable (receivable) for monthly activity true-up	7.0	(16.4)
Big Spring refinery
Oil and Gas, Delivery Commitment [Line Items]
Revolving over/short inventory financing liability	30.7	73.5
Total Obligations Under Supply and Offtake Agreements	78.7	130.7
Less: Current portion	30.7	73.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	48.0	57.2
Other current payable (receivable) for monthly activity true-up	(8.8)	(3.1)
Krotz Spring Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability		87.6
Revolving over/short inventory financing liability	4.7	40.5
Total Obligations Under Supply and Offtake Agreements	73.8	128.1
Less: Current portion	4.7	40.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	69.1	87.6
Other current payable (receivable) for monthly activity true-up	7.4	(3.5)
Baseline Step-Out Liability
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	215.0	270.3
Baseline Step-Out Liability | El Dorado Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	97.9
Baseline Step-Out Liability | Big Spring refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	48.0	$ 57.2
Baseline Step-Out Liability | Krotz Spring Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	$ 69.1