Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net earnings	$ 400,904	$ 300,956
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	321,807	281,198
Share-based compensation	37,184	30,953
Loss on sale of revenue equipment and other	8,441	5,716
Deferred income taxes	(23,442)	(43,801)
Changes in operating assets and liabilities:
Trade accounts receivable	(174,871)	(113,432)
Other assets	4,647	58,230
Trade accounts payable	77,257	100,020
Income taxes payable or receivable	72,926	8,350
Claims accruals	25,043	7,901
Accrued payroll and other accrued expenses	27,707	(7,542)
Net cash provided by operating activities	777,603	628,549
Cash flows from investing activities:
Additions to property and equipment	(676,097)	(328,218)
Net proceeds from sale of equipment	91,120	13,380
Business acquisition		(137,630)
Changes in other assets	(1,278)	(3,641)
Net cash used in investing activities	(586,255)	(456,109)
Cash flows from financing activities:
Proceeds from revolving lines of credit and other	2,407,462	2,108,891
Payments on revolving lines of credit and other	(2,409,000)	(2,006,001)
Purchase of treasury stock	(100,027)	(179,813)
Stock repurchased for payroll taxes and other	(18,023)	(18,067)
Dividends paid	(78,785)	(76,120)
Net cash used in financing activities	(198,373)	(171,110)
Net change in cash and cash equivalents	(7,025)	1,330
Cash and cash equivalents at beginning of period	14,612	6,377
Cash and cash equivalents at end of period	7,587	7,707
Supplemental disclosure of cash flow information:
Interest	31,479	24,641
Income taxes	81,334	187,313
Noncash investing activities
Accruals for equipment received	$ 30,843	$ 22,984