Condensed Consolidated Statements of Earnings (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operating revenues, excluding fuel surcharge revenues	$ 1,152,349	$ 1,038,940
Fuel surcharge revenues	254,559	252,647
Total operating revenues	1,406,908	1,291,587
Operating expenses:
Rents and purchased transportation	705,414	644,533
Salaries, wages and employee benefits	304,394	263,724
Fuel and fuel taxes	119,950	116,560
Depreciation and amortization	68,967	60,730
Operating supplies and expenses	50,788	44,914
Insurance and claims	15,832	12,770
General and administrative expenses, net of asset dispositions	9,925	10,985
Operating taxes and licenses	8,973	7,513
Communication and utilities	5,358	4,819
Total operating expenses	1,289,601	1,166,548
Operating income	117,307	125,039
Net interest expense	6,380	6,256
Earnings before income taxes	110,927	118,783
Income taxes	42,263	45,434
Net earnings	$ 68,664	$ 73,349
Weighted average basic shares outstanding (in Shares)	117,250	117,553
Basic earnings per share (in Dollars per share)	$ 0.59	$ 0.62
Weighted average diluted shares outstanding (in Shares)	118,943	119,825
Diluted earnings per share (in Dollars per share)	$ 0.58	$ 0.61
Dividends declared per common share (in Dollars per share)	$ 0.20