Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net earnings	$ 300,956	$ 314,534
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	281,198	269,717
Share-based compensation	30,953	30,173
(Gain)/Loss on sale of revenue equipment and other	5,716	2,357
Provision for deferred income taxes	(43,801)	(9,152)
Changes in operating assets and liabilities:
Trade accounts receivable	(113,432)	(118,404)
Other assets	58,230	50,319
Trade accounts payable	100,020	56,827
Income taxes payable or receivable	8,350	73,512
Claims accruals	7,901	22
Accrued payroll and other accrued expenses	(7,542)	14,058
Net cash provided by operating activities	628,549	683,963
Cash flows from investing activities:
Additions to property and equipment	(328,218)	(498,913)
Net proceeds from sale of equipment	13,380	140,159
Business acquisition	(137,630)
Changes in other assets	(3,641)	(17)
Net cash used in investing activities	(456,109)	(358,771)
Cash flows from financing activities:
Proceeds from revolving lines of credit and other	2,108,891	1,087,164
Payments on revolving lines of credit and other	(2,006,001)	(1,152,465)
Purchase of treasury stock	(179,813)	(174,760)
Stock option exercises and other	1,100	1,342
Stock repurchased for payroll taxes	(19,167)	(18,613)
Tax benefit of stock options exercised		6,532
Dividends paid	(76,120)	(74,477)
Net cash used in financing activities	(171,110)	(325,277)
Net change in cash and cash equivalents	1,330	(85)
Cash and cash equivalents at beginning of period	6,377	5,566
Cash and cash equivalents at end of period	7,707	5,481
Supplemental disclosure of cash flow information:
Interest	24,641	21,614
Income taxes	$ 187,313	$ 118,803