Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:
Net earnings	$ 264,486	$ 250,518
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	216,109	187,304
Share-based compensation	26,122	23,602
Gain on sale of revenue equipment and other	(5,413)	(4,625)
Provision for deferred income taxes	(10,315)	15,798
Changes in operating assets and liabilities:
Trade accounts receivable	(102,779)	(118,903)
Other assets	29,126	17,890
Trade accounts payable	39,070	37,396
Income taxes payable or receivable	7,500	2,120
Claims accruals	19,192	14,381
Accrued payroll and other accrued expenses	3,267	(14,253)
Net cash provided by operating activities	486,365	411,228
Cash flows from investing activities:
Additions to property and equipment	(599,824)	(372,564)
Net proceeds from sale of equipment	120,599	38,940
Changes in other assets	21	(35)
Net cash used in investing activities	(479,204)	(333,659)
Cash flows from financing activities:
Proceeds from issuances of long-term debt	499,642
Payments on long-term debt	(250,000)	(100,000)
Proceeds from revolving lines of credit and other	1,380,887	1,372,752
Payments on revolving lines of credit and other	(1,494,421)	(1,264,438)
Purchase of treasury stock	(75,000)	(64,723)
Stock option exercises and other	7,070	8,772
Stock repurchased for payroll taxes	(22,789)	(17,964)
Tax benefit of stock options exercised	17,645	23,637
Dividends paid	(70,167)	(35,226)
Net cash used in financing activities	(7,133)	(77,190)
Net change in cash and cash equivalents	28	379
Cash and cash equivalents at beginning of period	5,831	5,589
Cash and cash equivalents at end of period	5,859	5,968
Supplemental disclosure of cash flow information:
Interest	25,635	23,514
Income taxes	$ 136,116	$ 111,404