Consolidated Condensed Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Operations:
Net income	$ 22,846	$ 19,548
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation	48,155	45,114
Gain on disposition of revenue equipment	(5,124)	(4,053)
Deferred income taxes	4,695	3,723
Tax benefits from share-based payment arrangement exercises	146	350
Excess tax benefits from share-based payment arrangement exercises	(122)	(282)
Share-based payment arrangement compensation expense	862	1,047
Income before income taxes attributable to noncontrolling interest	84	467
Equity in earnings from affiliate	(203)
Changes in other current operating items:
Receivables	(7,725)	(10,764)
Prepaid expenses and other	2,501	2,240
Accounts payable and accrued liabilities	(252)	5,114
Insurance and claims accruals	(14)	285
Net cash provided by operating activities	65,849	62,789
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Decrease in cash and cash equivalents resulting from change to equity method of accounting	(1,924)
Other	(27)	(27)
Net cash used for investing activities	(64,728)	(77,606)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Borrowings under credit facility and long-term debt	77,546	14,216
Repayment of borrowings under credit facility and long-term debt	(79,451)	(14,216)
Dividends on common stock	(1,937)	(1,545)
Issuance of common stock from share-based payment arrangement exercises	282	616
Excess tax benefits from share-based payment arrangement exercises	122	282
Noncontrolling interest distributions	(84)	(230)
Net cash used for financing activities	(3,522)	(877)
NET CHANGE IN CASH AND CASH EQUIVALENTS	(2,401)	(15,694)
CASH AND CASH EQUIVALENTS:
Beginning of period	3,473	20,821
End of period	1,072	5,127
SUPPLEMENTAL NON-CASH DISCLOSURE:
Change in property and equipment not yet paid for	6,422	2,325
Cash paid for:
Interest	69	6
Income taxes	13,015	6,723
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from disposition of property, plant, and equipment	35,321	41,521
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from disposition of property, plant, and equipment	2	554
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	(85,864)	(107,904)
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	$ (12,236)	$ (11,750)