Consolidated Condensed Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Operations:
Net income	$ 13,030	$ 10,289
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation	29,577	27,600
Gain on disposition of revenue equipment	(2,704)	(1,735)
Deferred income taxes	2,611	7,274
Tax benefits from share-based payment arrangement exercises	350	164
Excess tax benefits from share-based payment arrangement exercises	(282)	(142)
Share-based payment arrangement compensation expense	791	595
Income before income taxes attributable to noncontrolling interest	406	390
Changes in other current operating items:
Receivables	(6,698)	(5,328)
Prepaid expenses and other	1,393	663
Accounts payable and accrued liabilities	2,166	5,203
Insurance and claims accruals	(628)	(2,517)
Net cash provided by operating activities	40,012	42,456
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Other	(18)	120
Net cash used for investing activities	(55,304)	(11,879)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Borrowings under credit facility and long-term debt	4,665	35,382
Repayment of borrowings under credit facility and long-term debt	(4,665)	(54,728)
Dividends on common stock	(993)	(878)
Issuance of common stock from share-based payment arrangement exercises	616	137
Excess tax benefits from share-based payment arrangement exercises	282	142
Noncontrolling interest distributions and other, net	(185)	131
Change in net checks issued in excess of cash balances		(1,066)
Net cash used for financing activities	(280)	(20,880)
NET CHANGE IN CASH AND CASH EQUIVALENTS	(15,572)	9,697
CASH AND CASH EQUIVALENTS:
Beginning of period	20,821	5,306
End of period	5,249	15,003
Cash paid (received) for:
Interest		32
Income taxes	4,267	(7,894)
Non-cash investing activities:
Change in property and equipment not yet paid for	5,954	1,010
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from disposition of property, plant, and equipment	31,106	16,967
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from disposition of property, plant, and equipment		73
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	(79,381)	(23,143)
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	$ (7,011)	$ (5,896)