Consolidated Condensed Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Operations:
Net income	$ 14,869	$ 13,030
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation	31,907	29,577
Gain on disposition of revenue equipment	(3,652)	(2,704)
Deferred income taxes	3,130	2,611
Tax benefits from share-based payment arrangement exercises	143	350
Excess tax benefits from share-based payment arrangement exercises	(119)	(282)
Share-based payment arrangement compensation expense	651	791
Income before income taxes attributable to noncontrolling interest	84	406
Equity in earnings from affiliate	(44)
Changes in other current operating items:
Receivables	(3,274)	(6,698)
Prepaid expenses and other	1,413	1,393
Accounts payable and accrued liabilities	2,511	2,166
Insurance and claims accruals	191	(628)
Net cash provided by operating activities	47,810	40,012
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Decrease in cash and cash equivalents resulting from change to equity method of accounting	(1,924)
Other	(18)	(18)
Net cash used for investing activities	(54,416)	(55,304)
CASH FLOWS PROVIDED BY (USED FOR) FINANCING ACTIVITIES:
Borrowings under credit facility and long-term debt	36,946	4,665
Repayment of borrowings under credit facility and long-term debt	(32,285)	(4,665)
Dividends on common stock	(1,107)	(993)
Issuance of common stock from share-based payment arrangement exercises	179	616
Excess tax benefits from share-based payment arrangement exercises	119	282
Noncontrolling interest distributions	(84)	(185)
Net cash provided by (used for) financing activities	3,768	(280)
NET CHANGE IN CASH AND CASH EQUIVALENTS	(2,838)	(15,572)
CASH AND CASH EQUIVALENTS:
Beginning of period	3,473	20,821
End of period	635	5,249
SUPPLEMENTAL NON-CASH DISCLOSURE:
Change in property and equipment not yet paid for	9,560	5,954
Cash paid for:
Interest	30
Income taxes	7,754	4,267
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from disposition of property, plant, and equipment	25,631	31,106
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	(68,461)	(79,381)
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	$ (9,646)	$ (7,011)