Consolidated Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 19,529	$ 15,428
Accounts receivable, trade, less allowance of $10,592 and $10,528, respectively	219,010	211,133
Other receivables	9,621	8,004
Inventories and supplies	22,528	23,260
Prepaid taxes, licenses and permits	11,088	14,893
Current deferred income taxes	24,869	25,139
Other current assets	21,229	21,330
Total current assets	327,874	319,187
Property and equipment	1,688,715	1,690,490
Less – accumulated depreciation	715,878	696,647
Property and equipment, net	972,837	993,843
Other non-current assets	22,263	21,870
Total assets	1,322,974	1,334,900
Current liabilities:
Accounts payable	62,724	56,397
Current portion of long-term debt	0	20,000
Insurance and claims accruals	61,155	57,679
Accrued payroll	23,556	21,134
Income taxes payable	14,491	1,544
Other current liabilities	18,849	19,439
Total current liabilities	180,775	176,193
Long-term debt, net of current portion	40,000	70,000
Other long-term liabilities	16,341	15,779
Insurance and claims accruals, net of current portion	127,950	125,500
Deferred income taxes	226,833	232,531
Commitments and contingencies
Stockholders' equity:
Common stock, $0.01 par value, 200,000,000 shares authorized; 80,533,536 shares issued; 73,272,124 and 73,246,598 shares outstanding, respectively	805	805
Paid-in capital	98,403	97,457
Retained earnings	772,464	758,617
Accumulated other comprehensive loss	(3,193)	(4,156)
Treasury stock, at cost; 7,261,412 and 7,286,938 shares, respectively	(137,404)	(137,826)
Total stockholders' equity	731,075	714,897
Total liabilities and stockholders' equity	$ 1,322,974	$ 1,334,900