Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating revenues	$ 2,463,701	$ 2,457,914	$ 2,116,737
Operating expenses:
Salaries, wages and benefits	818,487	781,064	681,547
Fuel	235,928	254,564	198,745
Supplies and maintenance	182,909	185,074	164,325
Taxes and licenses	95,525	87,318	86,768
Insurance and claims	88,913	98,133	79,927
Depreciation	249,527	230,151	217,639
Rent and purchased transportation	549,438	589,002	509,573
Communications and utilities	15,303	16,063	16,105
Other	2,199	(7,670)	18,288
Total operating expenses	2,238,229	2,233,699	1,972,917
Operating income	225,472	224,215	143,820
Other expense (income):
Interest expense	6,854	2,695	2,243
Interest income	(3,326)	(2,737)	(3,308)
Other	38	376	328
Total other expense (income)	3,566	334	(737)
Income before income taxes	221,906	223,881	144,557
Income tax expense (benefit)	54,962	55,733	(58,332)
Net income	$ 166,944	$ 168,148	$ 202,889
Earnings per share:
Basic	$ 2.40	$ 2.35	$ 2.81
Diluted	$ 2.38	$ 2.33	$ 2.80
Weighted-average common shares outstanding:
Basic	69,567	71,694	72,270
Diluted	70,026	72,057	72,558