Consolidated Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 27,714	$ 23,678
Accounts receivable, trade, less allowance of $10,166 and $9,939, respectively	261,305	231,647
Other receivables	20,888	10,769
Inventories and supplies	15,088	15,743
Prepaid taxes, licenses and permits	6,894	15,064
Current deferred income taxes	26,389	25,315
Other current assets	32,248	27,445
Total current assets	390,526	349,661
Property and equipment	1,724,963	1,727,737
Less – accumulated depreciation	762,991	750,219
Property and equipment, net	961,972	977,518
Other non-current assets	38,372	26,918
Total assets	1,390,870	1,354,097
Current liabilities:
Accounts payable	84,902	66,678
Insurance and claims accruals	62,301	59,811
Accrued payroll	27,250	22,785
Other current liabilities	20,292	18,457
Total current liabilities	194,745	167,731
Long-term debt, net of current portion	40,000	40,000
Other long-term liabilities	19,085	14,710
Insurance and claims accruals, net of current portion	132,250	131,900
Deferred income taxes	217,779	227,237
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.01 par value, 200,000,000 shares authorized; 80,533,536 shares issued; 71,950,164 and 72,713,920 shares outstanding, respecitvely	805	805
Paid-in capital	101,419	98,534
Retained earnings	863,596	830,842
Accumulated other comprehensive loss	(4,531)	(4,631)
Treasury stock, at cost; 8,583,372 and 7,819,616 shares, respectively	(174,278)	(153,031)
Total stockholders’ equity	787,011	772,519
Total liabilities and stockholders’ equity	$ 1,390,870	$ 1,354,097