Consolidated Income Statements - USD ($) shares in Thousands, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Revenues
Sales and other operating revenues		$ 3,460,200	$ 3,657,600	$ 3,800,400	$ 3,116,400	$ 3,501,700	$ 3,788,000	$ 3,829,000	$ 3,244,200	$ 14,034,600	$ 14,362,900	$ 12,826,600
Operating Expenses
Station and other operating expenses										559,300	541,300	514,900
Depreciation and amortization										152,200	134,000	116,900
Selling, general and administrative										144,600	136,200	141,200
Accretion of asset retirement obligations										2,100	2,000	1,800
Total operating expenses										13,766,300	14,087,100	12,539,400
Net settlement proceeds										100	50,400	0
Gain (loss) on sale of assets										100	(1,100)	(3,900)
Income from operations										268,500	325,100	283,300
Other income (expense)
Interest income										3,200	1,500	1,300
Interest expense										(54,900)	(52,900)	(46,700)
Loss on early debt extinguishment										(14,800)	0	0
Other nonoperating income (expense)										400	200	2,200
Total other income (expense)										(66,100)	(51,200)	(43,200)
Income before income taxes		61,900	91,300	43,300	5,900	100,500	57,000	69,100	47,300	202,400	273,900	240,100
Income tax expense (benefit)										47,600	60,300	(5,200)
Net Income		$ 47,600	$ 69,200	$ 32,700	$ 5,300	$ 77,500	$ 45,000	$ 51,800	$ 39,300	$ 154,800	$ 213,600	$ 245,300
Basic and Diluted Earnings Per Common Share:
Basic (in dollars per share)		$ 1.56	$ 2.20	$ 1.02	$ 0.16	$ 2.40	$ 1.40	$ 1.59	$ 1.17	$ 4.90	$ 6.54	$ 6.85
Diluted (in dollars per share)		$ 1.54	$ 2.18	$ 1.01	$ 0.16	$ 2.38	$ 1.38	$ 1.58	$ 1.16	$ 4.86	$ 6.48	$ 6.78
Weighted-average shares outstanding (in thousands):
Basic (in shares)										31,594	32,674	35,816
Diluted (in shares)										31,858	32,983	36,156
Supplemental information:
Excise taxes										$ 1,933,300	$ 1,838,900	$ 1,973,100
Petroleum product sales
Operating Revenues
Sales and other operating revenues	[1]									11,373,800	11,858,400	10,287,900
Operating Expenses
Operating expenses	[1]									10,707,400	11,251,100	9,773,200
Merchandise
Operating Revenues
Sales and other operating revenues										2,620,100	2,423,000	2,372,700
Operating Expenses
Operating expenses										2,200,700	2,022,500	1,991,400
Other operating revenues
Operating Revenues
Sales and other operating revenues										$ 40,700	$ 81,500	$ 166,000

[1] Years Ended December 31,(Millions of dollars except per share amounts)2019 2018 2017 Supplemental information: 1 Includes excise taxes of:$1,933.3 $1,838.9 $1,973.1