Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net earnings	$ 314,534	$ 310,490
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	269,717	251,239
Share-based compensation	30,173	27,010
(Gain)/Loss on sale of revenue equipment and other	2,357	(1,257)
Provision for deferred income taxes	(9,152)	(5,395)
Changes in operating assets and liabilities:
Trade accounts receivable	(132,936)	(17,603)
Other assets	64,851	35,591
Trade accounts payable	56,827	27,644
Income taxes payable or receivable	73,512	75,150
Claims accruals	22	3,930
Accrued payroll and other accrued expenses	14,058	(9,839)
Net cash provided by operating activities	683,963	696,960
Cash flows from investing activities:
Additions to property and equipment	(498,913)	(561,774)
Net proceeds from sale of equipment	140,159	131,114
Changes in other assets	(17)	(20,095)
Net cash used in investing activities	(358,771)	(450,755)
Cash flows from financing activities:
Proceeds from issuances of long-term debt		349,129
Payments on long-term debt		(250,000)
Proceeds from revolving lines of credit and other	1,087,164	1,576,329
Payments on revolving lines of credit and other	(1,152,465)	(1,629,244)
Purchase of treasury stock	(174,760)	(212,227)
Stock option exercises and other	1,342	2,501
Stock repurchased for payroll taxes	(18,613)	(24,263)
Tax benefit of stock options exercised	6,532	14,446
Dividends paid	(74,477)	(73,295)
Net cash used in financing activities	(325,277)	(246,624)
Net change in cash and cash equivalents	(85)	(419)
Cash and cash equivalents at beginning of period	5,566	5,961
Cash and cash equivalents at end of period	5,481	5,542
Supplemental disclosure of cash flow information:
Interest	21,614	25,290
Income taxes	$ 118,803	$ 103,832