Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 5,968	$ 5,589
Trade accounts receivable, net	584,914	466,011
Prepaid expenses and other	57,150	82,932
Total current assets	648,032	554,532
Property and equipment, at cost	3,150,319	2,904,706
Less accumulated depreciation	1,112,933	1,019,232
Net property and equipment	2,037,386	1,885,474
Other assets	27,016	24,635
Total assets	2,712,434	2,464,641
Current liabilities:
Current portion of long-term debt	250,000	100,000
Trade accounts payable	304,799	266,722
Claims accruals	61,823	47,442
Accrued payroll	61,173	70,647
Other accrued expenses	11,793	17,199
Deferred income taxes	750	750
Total current liabilities	690,338	502,760
Long-term debt	437,474	585,347
Other long-term liabilities	56,723	53,050
Deferred income taxes	547,422	531,624
Stockholders' equity	980,477	791,860
Total liabilities and stockholders' equity	$ 2,712,434	$ 2,464,641