Consolidated Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Revenue Equipment [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of assets	$ (7,462)	$ (4,843)
Cash flows used for investing activities:
Revenue equipment additions	(111,503)	(139,788)
Proceeds from revenue equipment dispositions	48,097	43,451
Buildings And Land Office Equipment And Other [Member]
Cash flows used for investing activities:
Revenue equipment additions	(5,416)	(11,784)
Proceeds from revenue equipment dispositions	13	4,625
Net income	25,161	26,955
Depreciation	61,205	55,469
Gain on disposition of assets		(3,712)
Deferred income taxes	10,246	(383)
Tax (deficiencies) benefits from share-based payment arrangement exercises	(55)	451
Excess tax benefits from share-based payment arrangement exercises	(129)	(432)
Share-based payment arrangement compensation expense	741	1,189
Equity in loss from affiliate	621	184
Receivables	8,251	15,300
Prepaid expenses and other	1,419	1,057
Accounts payable and accrued liabilities	2,617	9,353
Insurance and claims accruals	1,526	834
Net cash provided by operating activities	104,141	101,422
Other	(33)	(30)
Net cash used for investing activities	(68,842)	(103,526)
Cash flows (used for) provided by financing activities:
Borrowings under credit facility and long-term debt	130,128	94,437
Repayment of borrowings under credit facility and long-term debt	(159,446)	(92,530)
Repurchase and retirement of common stock	(7,513)
Dividends on common stock	(2,436)	(2,518)
Issuance of common stock from share-based payment arrangement exercises	3,508	2,363
Excess tax benefits from share-based payment arrangement exercises	129	432
Employee taxes paid in exchange for shares withheld	(127)
Change in checks issued in excess of cash balances	199	(58)
Net cash (used for) provided by financing activities	(35,558)	2,126
Net change in cash and cash equivalents	(259)	22
Cash and cash equivalents:
Beginning of period	434	123
End of period	175	145
Supplemental non-cash disclosure:
Change in property and equipment not yet paid	9,281	10,237
Income taxes	(2,595)	(4,451)
Interest	$ 174	$ 136