Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net earnings	$ 205,109	$ 195,351
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	178,716	165,038
Share-based compensation	22,915	20,697
Loss on sale of revenue equipment and other	1,030	147
Benefit from deferred income taxes	2,354	(11,283)
Changes in operating assets and liabilities:
Trade accounts receivable	(84,184)	(11,446)
Other assets	41,982	14,964
Trade accounts payable	11,267	17,701
Income taxes payable or receivable	72,041	73,073
Claims accruals	11,408	1,704
Accrued payroll and other accrued expenses	11,500	(12,409)
Net cash provided by operating activities	474,138	453,537
Cash flows from investing activities:
Additions to property and equipment	(351,507)	(381,681)
Net proceeds from sale of equipment	93,549	82,435
Changes in other assets	(7)	(20,097)
Net cash used in investing activities	(257,965)	(319,343)
Cash flows from financing activities:
Proceeds from revolving lines of credit and other	676,687	977,630
Payments on revolving lines of credit and other	(738,198)	(1,030,833)
Purchase of treasury stock	(100,000)	(34,357)
Stock option exercises and other	1,342	1,193
Stock repurchased for payroll taxes	(975)	(955)
Tax benefit of stock options exercised	280	1,698
Dividends paid	(49,598)	(48,945)
Net cash used in financing activities	(210,462)	(134,569)
Net change in cash and cash equivalents	5,711	(375)
Cash and cash equivalents at beginning of period	5,566	5,961
Cash and cash equivalents at end of period	11,277	5,586
Cash paid during the period for:
Interest	12,855	13,435
Income taxes	$ 49,039	$ 54,816