Benefit Plans - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Requisite service period	30 days
Minimum participant age	21 years
Employer matching contribution, percent of match	6.00%
Employers matching contribution, vesting percentage	100.00%
Total plan contributions	$ 5,600,000	$ 4,000,000.0	$ 3,600,000
Period with five consecutive years of highest average compensation	10 years
U.S. Oil plan
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions, next fiscal year	$ 500,000
Wyoming Refining plan
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions, next fiscal year	$ 0