Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating revenues	$ 649,814	$ 568,959	$ 1,266,260	$ 1,161,662
Operating expenses:
Salaries, wages and benefits	210,095	194,981	414,948	400,978
Fuel	58,503	30,677	109,341	79,448
Supplies and maintenance	49,414	43,343	95,561	89,064
Taxes and licenses	23,744	23,953	46,977	46,803
Insurance and claims	20,739	25,789	42,795	61,853
Depreciation	63,865	67,670	127,816	136,507
Rent and purchased transportation	150,920	120,704	297,413	247,146
Communications and utilities	3,333	3,536	6,355	7,344
Other	(7,662)	5,488	(14,280)	8,635
Total operating expenses	572,951	516,141	1,126,926	1,077,778
Operating income	76,863	52,818	139,334	83,884
Other expense (income):
Interest expense	701	1,161	1,539	2,752
Interest income	(334)	(377)	(631)	(1,003)
Gain on equity investment	(20,191)	0	(20,191)	0
Other	54	23	96	68
Total other expense (income)	(19,770)	807	(19,187)	1,817
Income before income taxes	96,633	52,011	158,521	82,067
Income taxes	24,601	12,879	39,997	19,877
Net income	$ 72,032	$ 39,132	$ 118,524	$ 62,190
Earnings per share:
Basic	$ 1.06	$ 0.57	$ 1.74	$ 0.90
Diluted	$ 1.06	$ 0.56	$ 1.74	$ 0.89
Weighted-average common shares outstanding:
Basic	67,926	69,093	67,929	69,173
Diluted	68,216	69,435	68,237	69,531