Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating revenues	$ 568,959	$ 627,533	$ 1,161,662	$ 1,223,650
Operating expenses:
Salaries, wages and benefits	194,981	206,001	400,978	408,800
Fuel	30,677	61,064	79,448	117,202
Supplies and maintenance	43,343	44,371	89,064	90,056
Taxes and licenses	23,953	23,643	46,803	46,544
Insurance and claims	25,789	20,992	61,853	43,701
Depreciation	67,670	61,437	136,507	122,196
Rent and purchased transportation	120,704	146,176	247,146	279,012
Communications and utilities	3,536	3,903	7,344	7,914
Other	5,488	1,504	8,635	1,764
Total operating expenses	516,141	569,091	1,077,778	1,117,189
Operating income	52,818	58,442	83,884	106,461
Other expense (income):
Interest expense	1,161	1,429	2,752	2,287
Interest income	(377)	(989)	(1,003)	(1,892)
Other	23	58	68	(58)
Total other expense (income)	807	498	1,817	337
Income before income taxes	52,011	57,944	82,067	106,124
Income taxes	12,879	14,626	19,877	26,720
Net income	$ 39,132	$ 43,318	$ 62,190	$ 79,404
Earnings per share:
Basic	$ 0.57	$ 0.62	$ 0.90	$ 1.14
Diluted	$ 0.56	$ 0.62	$ 0.89	$ 1.13
Weighted-average common shares outstanding:
Basic	69,093	69,593	69,173	69,932
Diluted	69,435	69,893	69,531	70,229