Consolidated Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 56,468	$ 23,678
Accounts receivable, trade, less allowance of $10,032 and $9,939, respectively	244,294	231,647
Other receivables	11,680	10,769
Inventories and supplies	14,519	15,743
Prepaid taxes, licenses and permits	11,017	15,064
Current deferred income taxes	25,852	25,315
Other current assets	34,850	27,445
Total current assets	398,680	349,661
Property and equipment	1,705,581	1,727,737
Less – accumulated depreciation	758,892	750,219
Property and equipment, net	946,689	977,518
Other non-current assets	27,240	26,918
Total assets	1,372,609	1,354,097
Current liabilities:
Accounts payable	70,187	66,678
Insurance and claims accruals	64,764	59,811
Accrued payroll	25,385	22,785
Other current liabilities	30,162	18,457
Total current liabilities	190,498	167,731
Long-term debt, net of current portion	40,000	40,000
Other long-term liabilities	14,948	14,710
Insurance and claims accruals, net of current portion	130,700	131,900
Deferred income taxes	221,440	227,237
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.01 par value, 200,000,000 shares authorized; 80,533,536 shares issued; 72,389,330 and 72,713,920 shares outstanding, respecitvely	805	805
Paid-in capital	99,973	98,534
Retained earnings	841,561	830,842
Accumulated other comprehensive loss	(4,621)	(4,631)
Treasury stock, at cost; 8,144,206 and 7,819,616 shares, respectively	(162,695)	(153,031)
Total stockholders’ equity	775,023	772,519
Total liabilities and stockholders’ equity	$ 1,372,609	$ 1,354,097