Condensed Consolidated Statements of Earnings (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Operating revenues, excluding fuel surcharge revenues	$ 1,316,951	$ 1,165,965	$ 3,737,936	$ 3,325,070
Fuel surcharge revenues	284,205	269,885	817,994	785,225
Total operating revenues	1,601,156	1,435,850	4,555,930	4,110,295
Operating expenses:
Rents and purchased transportation	802,092	724,417	2,282,992	2,062,745
Salaries, wages and employee benefits	327,106	289,789	951,517	835,765
Fuel and fuel taxes	115,503	114,147	352,452	340,987
Depreciation and amortization	75,416	64,291	216,109	187,304
Operating supplies and expenses	56,978	55,378	165,939	149,918
Insurance and claims	21,904	13,878	57,622	38,759
General and administrative expenses, net of asset dispositions	15,057	10,172	36,525	33,581
Operating taxes and licenses	9,893	8,168	28,517	23,723
Communication and utilities	5,107	4,881	15,620	14,338
Total operating expenses	1,429,056	1,285,121	4,107,293	3,687,120
Operating income	172,100	150,729	448,637	423,175
Net interest expense	6,649	5,835	21,358	18,320
Earnings before income taxes	165,451	144,894	427,279	404,855
Income taxes	63,037	55,422	162,793	154,337
Net earnings	$ 102,414	$ 89,472	$ 264,486	$ 250,518
Weighted average basic shares outstanding (in Shares)	117,050	117,723	117,020	117,472
Basic earnings per share (in Dollars per share)	$ 0.87	$ 0.76	$ 2.26	$ 2.13
Weighted average diluted shares outstanding (in Shares)	118,221	119,357	118,567	119,552
Diluted earnings per share (in Dollars per share)	$ 0.87	$ 0.75	$ 2.23	$ 2.10
Dividends declared per common share (in Dollars per share)	$ 0.20	$ 0.15	$ 0.60	$ 0.30