Condensed Consolidated Statements of Earnings (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Operating revenues, excluding fuel surcharge revenues	$ 1,268,636	$ 1,120,164	$ 2,420,985	$ 2,159,104
Fuel surcharge revenues	279,231	262,694	533,789	515,340
Total operating revenues	1,547,867	1,382,858	2,954,774	2,674,444
Operating expenses:
Rents and purchased transportation	775,485	693,795	1,480,900	1,338,328
Salaries, wages and employee benefits	320,016	282,252	624,410	545,976
Fuel and fuel taxes	116,999	110,280	236,949	226,840
Depreciation and amortization	71,726	62,283	140,693	123,013
Operating supplies and expenses	58,173	49,626	108,961	94,540
Insurance and claims	19,886	12,111	35,718	24,881
General and administrative expenses, net of asset dispositions	11,547	12,425	21,470	23,409
Operating taxes and licenses	9,650	8,042	18,623	15,555
Communication and utilities	5,155	4,637	10,513	9,456
Total operating expenses	1,388,637	1,235,451	2,678,237	2,401,998
Operating income	159,230	147,407	276,537	272,446
Net interest expense	8,329	6,230	14,710	12,485
Earnings before income taxes	150,901	141,177	261,827	259,961
Income taxes	57,493	53,480	99,756	98,916
Net earnings	$ 93,408	$ 87,697	$ 162,071	$ 161,045
Weighted average basic shares outstanding (in Shares)	116,764	117,139	117,006	117,345
Basic earnings per share (in Dollars per share)	$ 0.80	$ 0.75	$ 1.39	$ 1.37
Weighted average diluted shares outstanding (in Shares)	118,541	119,472	118,740	119,647
Diluted earnings per share (in Dollars per share)	$ 0.79	$ 0.73	$ 1.36	$ 1.35
Dividends declared per common share (in Dollars per share)	$ 0.20	$ 0.15	$ 0.40	$ 0.15