Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 29,183	$ 12,857
Customer receivables, less allowances of $8,302 and $8,561, respectively	248,225	219,039
Other receivables	2,092	1,324
Prepaid expenses	26,140	21,754
Deferred income taxes	19,324	20,054
Total current assets	324,964	275,028
Property and equipment:
Revenue equipment	919,300	922,030
Land and structures	893,720	874,768
Other fixed assets	230,754	225,298
Leasehold improvements	6,051	6,128
Total property and equipment	2,049,825	2,028,224
Accumulated depreciation	(674,076)	(648,919)
Net property and equipment	1,375,749	1,379,305
Goodwill	19,463	19,463
Other assets	41,016	38,718
Total assets	1,761,192	1,712,514
Current liabilities:
Accounts payable	41,471	44,891
Compensation and benefits	81,158	80,047
Claims and insurance accruals	34,681	33,990
Other accrued liabilities	20,904	20,906
Income taxes payable	37,297	6,327
Current maturities of long-term debt	38,619	38,978
Total current liabilities	254,130	225,139
Long-term liabilities:
Long-term debt	180,714	201,429
Other non-current liabilities	111,106	106,791
Deferred income taxes	148,720	153,186
Total long-term liabilities	440,540	461,406
Total liabilities	694,670	686,545
Shareholders' equity:
Common stock - $0.10 par value, 140,000,000 shares authorized, 86,164,917 shares outstanding at March 31, 2013 and December 31, 2012	8,616	8,616
Capital in excess of par value	134,401	134,401
Retained earnings	923,505	882,952
Total shareholders' equity	1,066,522	1,025,969
Total liabilities and shareholders' equity	$ 1,761,192	$ 1,712,514