Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 5,659	$ 5,450
Trade accounts receivable, net	504,252	411,479
Prepaid expenses and other	53,346	96,613
Total current assets	563,257	513,542
Property and equipment, at cost	2,862,385	2,658,143
Less accumulated depreciation	1,013,932	931,273
Net property and equipment	1,848,453	1,726,870
Other assets	26,632	26,920
Total assets	2,438,342	2,267,332
Current liabilities:
Current portion of long-term debt	100,000	50,000
Trade accounts payable	328,757	251,625
Claims accruals	48,194	42,364
Accrued payroll	58,315	77,107
Other accrued expenses	13,409	17,419
Total current liabilities	548,675	438,515
Long-term debt	544,904	699,177
Other long-term liabilities	46,849	45,382
Deferred income taxes	516,724	516,715
Stockholders' equity	781,190	567,543
Total liabilities and stockholders' equity	$ 2,438,342	$ 2,267,332