Consolidated Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 24,248	$ 15,428
Accounts receivable, trade, less allowance of $10,540 and $10,528, respectively	223,990	211,133
Other receivables	10,453	8,004
Inventories and supplies	20,249	23,260
Prepaid taxes, licenses and permits	7,039	14,893
Current deferred income taxes	25,662	25,139
Other current assets	36,225	21,330
Total current assets	347,866	319,187
Property and equipment	1,671,280	1,690,490
Less – accumulated depreciation	721,800	696,647
Property and equipment, net	949,480	993,843
Other non-current assets	23,102	21,870
Total assets	1,320,448	1,334,900
Current liabilities:
Accounts payable	69,339	56,397
Current portion of long-term debt	0	20,000
Insurance and claims accruals	57,543	57,679
Accrued payroll	24,023	21,134
Other current liabilities	18,394	20,983
Total current liabilities	169,299	176,193
Long-term debt, net of current portion	40,000	70,000
Other long-term liabilities	16,799	15,779
Insurance and claims accruals, net of current portion	127,400	125,500
Deferred income taxes	228,069	232,531
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.01 par value, 200,000,000 shares authorized; 80,533,536 shares issued; 72,692,730 and 73,246,598 shares outstanding, respectively	805	805
Paid-in capital	99,681	97,457
Retained earnings	794,669	758,617
Accumulated other comprehensive loss	(4,340)	(4,156)
Treasury stock, at cost; 7,840,806 and 7,286,938 shares, respectively	(151,934)	(137,826)
Total stockholders’ equity	738,881	714,897
Total liabilities and stockholders’ equity	$ 1,320,448	$ 1,334,900