Consolidated Condensed Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operations:
Net income	$ 7,202	$ 5,446
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation	15,688	14,535
Gain on disposition of revenue equipment	(2,415)	(1,525)
Deferred income taxes	1,564	1,900
Tax benefits from share-based payment arrangement exercises		272
Excess tax benefits from share-based payment arrangement exercises		(215)
Share-based payment arrangement compensation expense	217	248
Income before income taxes attributable to noncontrolling interest	84	161
Changes in other current operating items:
Receivables	(307)	(693)
Prepaid expenses and other	1,783	1,150
Accounts payable and accrued liabilities	(1,572)	(2,464)
Insurance and claims accruals	(250)	964
Net cash provided by operating activities	21,994	19,779
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Decrease in cash and cash equivalents resulting from change to equity method of accounting	(1,924)
Other	91	(9)
Net cash used for investing activities	(13,085)	(15,173)
CASH FLOWS (USED FOR) PROVIDED BY FINANCING ACTIVITIES:
Borrowings under credit facility and long-term debt	2,649
Repayment of borrowings under credit facility and long-term debt	(5,375)
Dividends on common stock	(553)	(441)
Issuance of common stock from share-based payment arrangement exercises	22	541
Excess tax benefits from share-based payment arrangement exercises		215
Noncontrolling interest distributions and other	(84)	(104)
Net cash (used for) provided by financing activities	(3,341)	211
NET INCREASE IN CASH AND CASH EQUIVALENTS	5,568	4,817
CASH AND CASH EQUIVALENTS:
Beginning of period	3,473	20,821
End of period	9,041	25,638
SUPPLEMENTAL NON-CASH DISCLOSURE:
Change in property and equipment not yet paid for	15,861	13,931
Cash paid (received) for:
Interest	2
Income taxes	3,697	679
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	(23,989)	(28,587)
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	(1,743)	(3,947)
Revenue Equipment [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from disposition of property, plant, and equipment	14,478	17,370
Buildings And Land, Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Proceeds from disposition of property, plant, and equipment	$ 2