Consolidated Condensed Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES:
Net income	$ 10,188	$ 5,287
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	17,827	16,371
Deferred income taxes	2,306	1,076
Tax benefits from share-based payment arrangement exercises	178	50
Excess tax benefits from share-based payment arrangement exercises	(159)	(5)
Share-based payment arrangement compensation expense	273	211
Equity in earnings from affiliate	159	(37)
Changes in other current operating items:
Receivables	18,703	1,795
Prepaid expenses and other	1,692	1,908
Accounts payable and accrued liabilities	6,034	1,072
Insurance and claims accruals	834	443
Net cash provided by operating activities	53,162	27,508
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Other	(14)	(9)
Net cash used for investing activities	(6,762)	(21,384)
CASH FLOWS USED FOR FINANCING ACTIVITIES:
Borrowings under credit facility and long-term debt	13,444
Repayment of borrowings under credit facility and long-term debt	(37,817)
Dividends on common stock	(837)	(834)
Issuance of common stock from share-based payment arrangement exercises	973	370
Excess tax benefits from share-based payment arrangement exercises	159	5
Change in net checks issued in excess of cash balances	(745)
Net cash used for financing activities	(24,823)	(459)
NET CHANGE IN CASH AND CASH EQUIVALENTS	21,577	5,665
Beginning of period	123	13,650
End of period	21,700	19,315
SUPPLEMENTAL NON-CASH DISCLOSURE:
Change in property and equipment not yet paid	5,315	3,469
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Income taxes	(12,145)	2,347
Interest	28	24
Revenue Equipment [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of assets	(1,161)	(663)
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	(20,360)	(27,543)
Proceeds from disposition of property, plant, and equipment	13,291	9,850
Facility [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of assets	(3,712)
Buildings And Land Office Equipment And Other [Member]
CASH FLOWS USED FOR INVESTING ACTIVITIES:
Additions to property, plant, and equipment	(4,295)	(3,682)
Proceeds from disposition of property, plant, and equipment	$ 4,616