Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities:
Net earnings	$ 342,382	$ 310,354	$ 257,006
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	253,380	229,166	213,943
Share-based compensation	32,354	29,715	26,841
Gain on sale of revenue equipment and other	(5,334)	(16,845)	(14,109)
Provision for deferred income taxes	48,076	20,795	117,711
Changes in operating assets and liabilities:
Trade accounts receivable	(102,508)	(54,532)	(60,292)
Income taxes receivable or payable	(5,381)	11,868	9,045
Other assets	(23,254)	(4,826)	1,298
Trade accounts payable	11,530	15,097	56,179
Claims accruals	20,779	5,078	9,722
Accrued payroll and other accrued expenses	2,327	2,174	18,348
Net cash provided by operating activities	574,351	548,044	635,692
Cash flows from investing activities:
Additions to property and equipment	(493,431)	(439,494)	(502,282)
Proceeds from sale of equipment	50,927	69,815	56,413
Change in other assets	(37)	85	340
Net cash used in investing activities	(442,541)	(369,594)	(445,529)
Cash flows from financing activities:
Proceeds from issuances of long-term debt			200,000
Payments on long-term debt	(100,000)	(50,000)	(200,000)
Proceeds from revolving lines of credit and other	1,933,753	1,605,674	1,097,657
Payments on revolving lines of credit and other	(1,811,177)	(1,618,233)	(1,000,696)
Purchase of treasury stock	(114,723)	(50,000)	(246,406)
Stock option exercises and other	9,403	11,240	11,465
Stock repurchased for payroll taxes	(17,963)	(13,651)	(7,703)
Tax benefit of stock options exercised	21,950	20,090	15,562
Dividends paid	(52,811)	(83,431)	(62,243)
Net cash used in financing activities	(131,568)	(178,311)	(192,364)
Net increase/(decrease) in cash and cash equivalents	242	139	(2,201)
Cash and cash equivalents at beginning of year	5,589	5,450	7,651
Cash and cash equivalents at end of year	5,831	5,589	5,450
Cash paid during the year for:
Interest	24,722	27,070	30,733
Income taxes	$ 141,968	$ 132,096	$ 16,377