Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities:
Net earnings	$ 68,664	$ 73,349
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	68,967	60,730
Share-based compensation	9,972	9,137
Gain on sale of revenue equipment and other	(2,691)	(1,307)
Deferred income taxes	(5,287)	4,398
Changes in operating assets and liabilities:
Trade accounts receivable	(66,592)	(63,322)
Other assets	8,259	(4,166)
Trade accounts payable	35,038	108,246
Income taxes payable or receivable	42,764	37,379
Claims accruals	8,826	2,408
Accrued payroll and other accrued expenses	(8,875)	(20,093)
Net cash provided by operating activities	159,045	206,759
Cash flows from investing activities:
Additions to property and equipment	(198,264)	(125,537)
Net proceeds from sale of equipment	40,052	10,479
Change in other assets		(12)
Net cash used in investing activities	(158,212)	(115,070)
Cash flows from financing activities:
Proceeds from issuances of long-term debt	499,642
Payments on long-term debt	(150,000)	(50,000)
Proceeds from revolving lines of credit and other	397,946	302,643
Payments on revolving lines of credit and other	(607,078)	(345,600)
Stock option exercises and other	267	406
Stock repurchased for payroll taxes	(99)	(46)
Tax benefit of stock options exercised	320	1,066
Dividends paid	(23,450)
Net cash provided by/(used in) financing activities	117,548	(91,531)
Net change in cash and cash equivalents	118,381	158
Cash and cash equivalents at beginning of period	5,831	5,589
Cash and cash equivalents at end of period	124,212	5,747
Cash paid during the period for:
Interest	8,802	10,846
Income taxes	$ 3,663	$ 2,047