Consolidated Statements of Earnings - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating revenues, excluding fuel surcharge revenues	$ 6,435,858	$ 6,007,347	$ 5,516,282
Fuel surcharge revenues	753,710	548,112	671,364
Total operating revenues	7,189,568	6,555,459	6,187,646
Operating expenses:
Rents and purchased transportation	3,650,806	3,255,692	2,994,586
Salaries, wages and employee benefits	1,608,378	1,469,187	1,394,239
Depreciation and amortization	383,518	361,510	339,613
Fuel and fuel taxes	347,573	283,437	313,034
Operating supplies and expenses	257,239	233,223	220,597
General and administrative expenses, net of asset dispositions	125,878	87,053	72,522
Insurance and claims	123,579	78,410	73,689
Operating taxes and licenses	44,825	45,954	43,084
Communication and utilities	23,983	19,973	20,588
Total operating expenses	6,565,779	5,834,439	5,471,952
Operating income	623,789	721,020	715,694
Interest income	235	71	86
Interest expense	28,785	25,294	25,577
Earnings before income taxes	595,239	695,797	690,203
Income taxes	(91,024)	263,707	262,968
Net earnings	$ 686,263	$ 432,090	$ 427,235
Weighted average basic shares outstanding (in shares)	109,987	112,474	115,677
Basic earnings per share (in dollars per share)	$ 6.24	$ 3.84	$ 3.69
Weighted average diluted shares outstanding (in shares)	111,049	113,361	116,728
Diluted earnings per share (in dollars per share)	$ 6.18	$ 3.81	$ 3.66
Dividends declared per common share (in dollars per share)	$ 0.92	$ 0.88	$ 0.84