Crude Oil Supply and Inventory Purchase Agreement - Payable (Receivable) Under Supply and Offtake Agreements (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Oil and Gas, Delivery Commitment [Line Items]
Revolving over/short product financing liability	$ 97.9	$ 207.0
Total Obligations Under Supply and Offtake Agreements	277.4	477.3
Less: Current portion	97.9	332.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	179.5	144.8
Other current payable (receivable) for monthly activity true-up	3.9	(23.0)
El Dorado Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability		125.5
Revolving over/short product financing liability	58.9	93.0
Total Obligations Under Supply and Offtake Agreements	137.6	218.5
Less: Current portion	58.9	218.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	78.7	0.0
Other current payable (receivable) for monthly activity true-up	11.4	(16.4)
Big Spring refinery
Oil and Gas, Delivery Commitment [Line Items]
Revolving over/short product financing liability	30.3	73.5
Total Obligations Under Supply and Offtake Agreements	72.0	130.7
Less: Current portion	30.3	73.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	41.7	57.2
Other current payable (receivable) for monthly activity true-up	10.7	(3.1)
Krotz Spring Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability		87.6
Revolving over/short product financing liability	8.7	40.5
Total Obligations Under Supply and Offtake Agreements	67.8	128.1
Less: Current portion	8.7	40.5
Obligations Under Supply and Offtake Agreements - Noncurrent portion	59.1	87.6
Other current payable (receivable) for monthly activity true-up	(18.2)	(3.5)
Baseline Step-Out Liability
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	179.5	270.3
Baseline Step-Out Liability | El Dorado Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	78.7
Baseline Step-Out Liability | Big Spring refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	41.7	$ 57.2
Baseline Step-Out Liability | Krotz Spring Refinery
Oil and Gas, Delivery Commitment [Line Items]
Baseline Step-Out Liability	$ 59.1