Consolidated Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Revenue Equipment [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition assets	$ (2,948)	$ (1,941)
Cash flows used for investing activities:
Additions to property, plant and equipment	(68,524)	(66,115)
Proceeds from disposition of property, plant and equipment	28,867	$ 21,439
Facility [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition assets	(3,712)
Buildings And Land Office Equipment And Other [Member]
Cash flows used for investing activities:
Additions to property, plant and equipment	(8,280)	$ (24,839)
Proceeds from disposition of property, plant and equipment	4,625
Net income	18,545	$ 13,213
Depreciation	36,138	33,236
Deferred income taxes	4,612	2,151
Tax benefits from share-based payment arrangement exercises	448	134
Excess tax benefits from share-based payment arrangement exercises	(428)	(90)
Share-based payment arrangement compensation expense	856	611
Equity in earnings from affiliate	143	(530)
Receivables	11,536	(7,205)
Prepaid expenses and other	948	1,325
Accounts payable and accrued liabilities	5,991	(817)
Insurance and claims accruals	(353)	608
Net cash provided by operating activities	71,776	40,695
Other	(23)	(18)
Net cash used for investing activities	(43,335)	(69,533)
Cash flows (used for) provided by financing activities:
Borrowings under credit facility and long-term debt	13,444	26,875
Repayment of borrowings under credit facility and long-term debt	(37,817)	(10,118)
Dividends on common stock	(1,678)	(1,669)
Issuance of common stock from share-based payment arrangement exercises	2,303	966
Excess tax benefits from share-based payment arrangement exercises	428	$ 90
Change in checks issued in excess of cash balances	(745)
Net cash (used for) provided by financing activities	(24,065)	$ 16,144
Net change in cash and cash equivalents	4,376	(12,694)
Cash and cash equivalents:
Beginning of period	123	13,650
End of period	4,499	956
Supplemental non-cash disclosure:
Change in property and equipment not yet paid	30,210	4,837
Supplemental disclosure of cash flow information:
Income taxes	(7,440)	11,765
Interest	$ 53	$ 47