Consolidated Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 17,350	$ 15,428
Accounts receivable, trade, less allowance of $10,022 and $10,528, respectively	236,858	211,133
Other receivables	12,677	8,004
Inventories and supplies	17,745	23,260
Prepaid taxes, licenses and permits	6,597	14,893
Current deferred income taxes	22,888	25,139
Other current assets	34,667	21,330
Total current assets	348,782	319,187
Property and equipment	1,712,627	1,690,490
Less – accumulated depreciation	736,984	696,647
Property and equipment, net	975,643	993,843
Other non-current assets	26,668	21,870
Total assets	1,351,093	1,334,900
Current liabilities:
Accounts payable	75,077	56,397
Current portion of long-term debt	0	20,000
Insurance and claims accruals	59,274	57,679
Accrued payroll	28,163	21,134
Other current liabilities	18,873	20,983
Total current liabilities	181,387	176,193
Long-term debt, net of current portion	50,000	70,000
Other long-term liabilities	13,963	15,779
Insurance and claims accruals, net of current portion	128,200	125,500
Deferred income taxes	224,865	232,531
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.01 par value, 200,000,000 shares authorized; 80,533,536 shares issued; 72,519,908 and 73,246,598 shares outstanding, respecitvely	805	805
Paid-in capital	100,164	97,457
Retained earnings	812,302	758,617
Accumulated other comprehensive loss	(4,291)	(4,156)
Treasury stock, at cost; 8,013,628 and 7,286,938 shares, respectively	(156,302)	(137,826)
Total stockholders’ equity	752,678	714,897
Total liabilities and stockholders’ equity	$ 1,351,093	$ 1,334,900