Consolidated Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Revenue Equipment [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of assets	$ (1,434)	$ (1,161)
Cash flows used for investing activities:
Revenue equipment additions	(18,865)	(20,360)
Proceeds from revenue equipment dispositions	10,526	13,291
Buildings And Land Office Equipment And Other [Member]
Cash flows used for investing activities:
Revenue equipment additions	$ (1,198)	(4,295)
Proceeds from revenue equipment dispositions		4,616
Net income	$ 8,193	10,188
Depreciation	$ 20,047	17,827
Gain on disposition of assets		(3,712)
Deferred income taxes	$ 3,680	2,306
Tax (deficiencies) benefits from share-based payment arrangement exercises	$ (169)	178
Excess tax benefits from share-based payment arrangement exercises		(159)
Share-based payment arrangement compensation expense	$ 290	273
Equity in loss from affiliate	129	159
Receivables	13,251	18,703
Prepaid expenses and other	1,305	1,692
Accounts payable and accrued liabilities	8,903	6,034
Insurance and claims accruals	870	834
Net cash provided by operating activities	55,065	53,162
Other	(16)	(14)
Net cash used for investing activities	(9,553)	(6,762)
Cash flows used for financing activities:
Borrowings under credit facility and long-term debt	36,225	13,444
Repayment of borrowings under credit facility and long-term debt	(74,092)	$ (37,817)
Repurchase and retirement of common stock	(7,513)
Dividends on common stock	(811)	$ (837)
Issuance of common stock from share-based payment arrangement exercises	$ 1,528	973
Excess tax benefits from share-based payment arrangement exercises		$ 159
Employee taxes paid in exchange for shares withheld	$ (127)
Change in checks issued in excess of cash balances		$ (745)
Net cash used for financing activities	$ (44,790)	(24,823)
Net change in cash and cash equivalents	722	21,577
Cash and cash equivalents:
Beginning of period	434	123
End of period	1,156	21,700
Supplemental non-cash disclosure:
Change in property and equipment not yet paid	114	5,315
Income taxes	(6,934)	(12,145)
Interest	$ 87	$ 28