Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 7,370	$ 12,857
Customer receivables, less allowances of $8,318 and $8,561, respectively	267,690	219,039
Other receivables	3,153	1,324
Prepaid expenses	26,264	21,754
Deferred income taxes	19,605	20,054
Total current assets	324,082	275,028
Property and equipment:
Revenue equipment	981,823	922,030
Land and structures	927,809	874,768
Other fixed assets	244,868	225,298
Leasehold improvements	6,160	6,128
Total property and equipment	2,160,660	2,028,224
Accumulated depreciation	(691,268)	(648,919)
Net property and equipment	1,469,392	1,379,305
Goodwill	19,463	19,463
Other assets	41,793	38,718
Total assets	1,854,730	1,712,514
Current liabilities:
Accounts payable	66,718	44,891
Compensation and benefits	89,262	80,047
Claims and insurance accruals	34,070	33,990
Other accrued liabilities	21,329	20,906
Income taxes payable	23,346	6,327
Current maturities of long-term debt	38,403	38,978
Total current liabilities	273,128	225,139
Long-term liabilities:
Long-term debt	190,394	201,429
Other non-current liabilities	111,627	106,791
Deferred income taxes	154,804	153,186
Total long-term liabilities	456,825	461,406
Total liabilities	729,953	686,545
Shareholders' equity:
Common stock - $0.10 par value, 140,000,000 shares authorized, 86,164,917 shares outstanding at June 30, 2013 and December 31, 2012	8,616	8,616
Capital in excess of par value	134,401	134,401
Retained earnings	981,760	882,952
Total shareholders' equity	1,124,777	1,025,969
Total liabilities and shareholders' equity	$ 1,854,730	$ 1,712,514