Condensed Consolidated Statements of Earnings (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating revenues, excluding fuel surcharge revenues	$ 1,538,701	$ 1,419,451	$ 4,448,709	$ 4,043,991
Fuel surcharge revenues	151,958	167,043	385,688	522,640
Total operating revenues	1,690,659	1,586,494	4,834,397	4,566,631
Operating expenses:
Rents and purchased transportation	846,238	770,148	2,381,547	2,194,683
Salaries, wages and employee benefits	374,517	351,651	1,108,997	1,030,438
Depreciation and amortization	91,001	86,201	269,717	251,239
Fuel and fuel taxes	74,179	76,755	205,082	243,459
Operating supplies and expenses	62,191	57,299	173,222	164,497
General and administrative expenses, net of asset dispositions	21,025	14,866	61,570	56,471
Insurance and claims	21,862	20,078	58,384	55,714
Operating taxes and licenses	11,665	10,683	34,156	31,505
Communication and utilities	5,004	4,967	15,063	15,824
Total operating expenses	1,507,682	1,392,648	4,307,738	4,043,830
Operating income	182,977	193,846	526,659	522,801
Net interest expense	6,485	7,838	19,347	21,202
Earnings before income taxes	176,492	186,008	507,312	501,599
Income taxes	67,067	70,869	192,778	191,109
Net earnings	$ 109,425	$ 115,139	$ 314,534	$ 310,490
Weighted average basic shares outstanding (in shares)	112,630	115,456	112,790	116,157
Basic earnings per share (in dollars per share)	$ 0.97	$ 1	$ 2.79	$ 2.67
Weighted average diluted shares outstanding (in shares)	113,363	116,282	113,709	117,293
Diluted earnings per share (in dollars per share)	$ 0.97	$ 0.99	$ 2.77	$ 2.65
Dividends declared per common share (in dollars per share)	$ 0.22	$ 0.21	$ 0.66	$ 0.63