Commitments and Contingencies - Bonds, Leases, and Sales and Purchase Commitments (Details) bbl in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) bbl	Dec. 31, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Outstanding bonds	$ 53.1	$ 73.0
Sales commitments under derivative programs	372.6
Purchase commitments under derivative programs	$ 73.6
Minimum | Aviation Fuel
Long-term Purchase Commitment [Line Items]
Minimum purchase required (in barrels) | bbl	1,790
Maximum | Aviation Fuel
Long-term Purchase Commitment [Line Items]
Minimum purchase required (in barrels) | bbl	2,020