Consolidated Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 59,263	$ 22,604
Accounts receivable, trade, less allowance of $9,933 and $10,017, respectively	246,353	266,727
Other receivables	22,179	20,316
Inventories and supplies	17,490	17,824
Prepaid taxes, licenses and permits	11,325	14,914
Current deferred income taxes	36,048	34,066
Income taxes receivable	7,686	23,435
Other current assets	25,250	26,458
Total current assets	425,594	426,344
Property and equipment	1,820,703	1,786,229
Less – accumulated depreciation	770,417	772,447
Property and equipment, net	1,050,286	1,013,782
Other non-current assets	42,644	40,336
Total assets	1,518,524	1,480,462
Current liabilities:
Accounts payable	72,565	64,827
Insurance and claims accruals	73,625	73,814
Accrued payroll	31,827	28,121
Other current liabilities	20,233	19,768
Total current liabilities	198,250	186,530
Long-term debt, net of current portion	75,000	75,000
Other long-term liabilities	21,399	20,021
Insurance and claims accruals, net of current portion	128,845	123,445
Deferred income taxes	240,265	241,606
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.01 par value, 200,000,000 shares authorized; 80,533,536 shares issued; 72,102,651 and 72,038,368 shares outstanding, respecitvely	805	805
Paid-in capital	102,967	101,803
Retained earnings	934,622	915,085
Accumulated other comprehensive loss	(10,298)	(9,375)
Treasury stock, at cost; 8,430,885 and 8,495,168 shares, respectively	(173,331)	(174,458)
Total stockholders’ equity	854,765	833,860
Total liabilities and stockholders’ equity	$ 1,518,524	$ 1,480,462