Condensed Consolidated Statements of Cash Flows (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Cash flows from operating activities:
Net earnings	$ 115,791	$ 89,594
Depreciation and amortization	103,908	97,160
Share-based compensation	12,633	10,786
Gain on sale of revenue equipment and other	(6,129)	(3,032)
Impairment on assets held for sale		180
Provision for deferred income taxes	13,049	4,218
Changes in operating assets and liabilities:
Trade accounts receivable	(89,568)	(53,330)
Income tax payable	41,756	8,492
Other assets	24,270	19,295
Trade accounts payable	81,055	9,314
Claims accruals	4,205	6,591
Accrued payroll and other accrued expenses	6,703	19,562
Net cash provided by operating activities	307,673	208,830
Cash flows from investing activities:
Additions to property and equipment	(240,354)	(130,768)
Net proceeds from sale of equipment	29,391	26,823
Changes in other assets	86	(52)
Net cash used in investing activities	(210,877)	(103,997)
Cash flows from financing activities:
Proceeds from issuances of long-term debt	200,000
Payments on long-term debt	(200,000)
Proceeds from revolving lines of credit and other	412,208	712,300
Payments on revolving lines of credit and other	(402,400)	(662,529)
Purchase of treasury stock	(85,331)	(131,808)
Stock option exercises and other	4,915	2,977
Tax benefit on stock options exercised	8,703	4,351
Dividends paid	(31,393)	(30,253)
Net cash used in financing activities	(93,298)	(104,962)
Net change in cash and cash equivalents	3,498	(129)
Cash and cash equivalents at beginning of period	7,651	7,843
Cash and cash equivalents at end of period	11,149	7,714
Cash paid during the period for:
Interest	17,775	13,092
Income taxes	$ 8,126	$ 38,820