Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating revenues	$ 528,643	$ 508,676	$ 1,549,372	$ 1,490,159
Operating expenses:
Salaries, wages and benefits	170,238	162,862	500,620	479,298
Fuel	50,266	40,638	140,551	112,034
Supplies and maintenance	41,986	41,027	120,276	130,559
Taxes and licenses	21,671	21,540	64,095	64,353
Insurance and claims	20,669	19,106	60,336	59,384
Depreciation	53,578	51,781	162,619	152,849
Rent and purchased transportation	126,087	133,876	377,146	379,155
Communications and utilities	4,199	4,206	12,158	12,110
Other	4,075	4,566	12,812	9,303
Total operating expenses	492,769	479,602	1,450,613	1,399,045
Operating income	35,874	29,074	98,759	91,114
Other expense (income):
Interest expense	492	749	1,892	1,839
Interest income	(766)	(1,055)	(2,556)	(3,154)
Other	88	46	293	148
Total other income	(186)	(260)	(371)	(1,167)
Income before income taxes	36,060	29,334	99,130	92,281
Income taxes	13,543	10,414	37,375	34,963
Net income	$ 22,517	$ 18,920	$ 61,755	$ 57,318
Earnings per share:
Basic	$ 0.31	$ 0.26	$ 0.85	$ 0.80
Diluted	0.31	0.26	0.85	0.79
Dividends declared per share	$ 0.070	$ 0.060	$ 0.200	$ 0.180
Weighted-average common shares outstanding:
Basic	72,298	72,058	72,239	72,043
Diluted	72,601	72,406	72,517	72,364