Consolidated Condensed Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operations:
Net income	$ 5,287	$ 7,202
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	16,371	15,688
Gain on disposition of revenue equipment	(663)	(2,415)
Deferred income taxes	1,076	1,564
Tax benefits from share-based payment arrangement exercises	50
Excess tax benefits from share-based payment arrangement exercises	(5)
Share-based payment arrangement compensation expense	211	217
Income before income taxes attributable to noncontrolling interest		84
Equity in earnings from affiliate	(37)
Changes in other current operating items:
Receivables	1,795	(307)
Prepaid expenses and other	1,908	1,783
Accounts payable and accrued liabilities	1,072	(1,572)
Insurance and claims accruals	443	(250)
Net cash provided by operating activities	27,508	21,994
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Decrease in cash and cash equivalents resulting from change to equity method of accounting		(1,924)
Other	(9)	91
Net cash used for investing activities	(21,384)	(13,085)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Dividends on common stock	(834)	(553)
Issuance of common stock from share-based payment arrangement exercises	370	22
Excess tax benefits from share-based payment arrangement exercises	5
Borrowings under credit facility and long-term debt		2,649
Repayment of borrowings under credit facility and long-term debt		(5,375)
Noncontrolling interest distributions		(84)
Net cash used for financing activities	(459)	(3,341)
NET CHANGE IN CASH AND CASH EQUIVALENTS	5,665	5,568
CASH AND CASH EQUIVALENTS:
Beginning of period	13,650	3,473
End of period	19,315	9,041
SUPPLEMENTAL NON-CASH DISCLOSURE:
Change in property and equipment not yet paid for	3,469	15,861
Cash paid for:
Interest	24	2
Income taxes	2,347	3,697
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from disposition of property, plant, and equipment	9,850	14,478
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from disposition of property, plant, and equipment		2
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	(27,543)	(23,989)
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	$ (3,682)	$ (1,743)