Consolidated Condensed Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Operations:
Net income	$ 5,446	$ 4,095
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation	14,535	13,516
Gain on disposition of revenue equipment	(1,525)	(768)
Deferred income taxes	1,900	2,857
Tax benefits from share-based payment arrangement exercises	272	167
Excess tax benefits from share-based payment arrangement exercises	(215)	(149)
Share-based payment arrangement compensation expense	248	238
Income before income taxes attributable to noncontrolling interest	161	137
Changes in other current operating items:
Receivables	(693)	3,792
Prepaid expenses and other	1,150	1,460
Accounts payable and accrued liabilities	(2,464)	3,142
Insurance and claims accruals	964	(496)
Net cash provided by operating activities	19,779	27,991
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Other	(9)	129
Net cash used for investing activities	(15,173)	(4,867)
CASH FLOWS PROVIDED BY (USED FOR) FINANCING ACTIVITIES:
Dividends on common stock	(441)	(439)
Issuance of common stock from share-based payment arrangement exercises	541	105
Excess tax benefits from share-based payment arrangement exercises	215	149
Noncontrolling interest distributions and other, net	(104)	208
Borrowings under credit facility and long-term debt		35,329
Repayment of borrowings under credit facility and long-term debt		(54,675)
Change in net checks issued in excess of cash balances		(1,066)
Net cash provided by (used for) financing activities	211	(20,389)
NET CHANGE IN CASH AND CASH EQUIVALENTS	4,817	2,735
CASH AND CASH EQUIVALENTS:
Beginning of period	20,821	5,306
End of period	25,638	8,041
Cash paid (received) for:
Interest		29
Income taxes	679	(8,517)
Non-cash investing activities:
Change in property and equipment not yet paid for	13,931	(460)
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from revenue equipment dispositions	17,370	7,453
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	(28,587)	(10,192)
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	$ (3,947)	$ (2,257)