Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating revenues	$ 519,508	$ 498,681	$ 1,020,729	$ 981,483
Operating expenses:
Salaries, wages and benefits	169,543	159,699	330,382	316,436
Fuel	45,129	39,336	90,285	71,396
Supplies and maintenance	40,058	42,417	78,290	89,532
Taxes and licenses	21,638	21,826	42,424	42,813
Insurance and claims	19,827	21,931	39,667	40,278
Depreciation	53,705	50,904	109,041	101,068
Rent and purchased transportation	124,634	127,303	251,059	245,279
Communications and utilities	3,887	3,995	7,959	7,904
Other	4,174	1,717	8,737	4,737
Total operating expenses	482,595	469,128	957,844	919,443
Operating income	36,913	29,553	62,885	62,040
Other expense (income):
Interest expense	624	596	1,400	1,090
Interest income	(876)	(1,109)	(1,790)	(2,099)
Other	152	57	205	102
Total other income	(100)	(456)	(185)	(907)
Income before income taxes	37,013	30,009	63,070	62,947
Income taxes	13,794	11,703	23,832	24,549
Net income	$ 23,219	$ 18,306	$ 39,238	$ 38,398
Earnings per share:
Basic	$ 0.32	$ 0.25	$ 0.54	$ 0.53
Diluted	0.32	0.25	0.54	0.53
Dividends declared per share	$ 0.070	$ 0.060	$ 0.130	$ 0.120
Weighted-average common shares outstanding:
Basic	72,227	72,048	72,209	72,036
Diluted	72,492	72,366	72,469	72,349