Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 148,877	$ 110,723
Accounts receivable, net of allowance for doubtful accounts of $3,599 and $3,513 at June 30, 2013 and December 31, 2012, respectively	501,824	465,517
Federal and state income taxes receivable	2,373
Inventory	23,960	26,889
Deferred tax assets, net	35,716	52,959
Other	60,529	43,903
Total current assets	773,279	699,991
Property and equipment, net	3,665,753	3,615,383
Goodwill and intangible assets	169,408	171,463
Deposits on equipment purchases	29,987	43,776
Other	25,289	26,298
Total assets	4,663,716	4,556,911
Current liabilities:
Accounts payable	198,114	188,823
Federal and state income taxes payable		6,158
Accrued expenses	146,101	158,632
Current portion of long-term debt	8,750	6,250
Total current liabilities	352,965	359,863
Long-term debt	687,500	692,500
Deferred tax liabilities, net	885,807	857,302
Other	6,604	6,589
Total liabilities	1,932,876	1,916,254
Commitments and contingencies (see Note 9)
Stockholders' equity:
Preferred stock, par value $.01; authorized 1,000,000 shares, no shares issued
Common stock, par value $.01; authorized 300,000,000 shares with 186,446,351 and 184,059,900 issued and 147,340,925 and 145,913,162 outstanding at June 30, 2013 and December 31, 2012, respectively	1,864	1,841
Additional paid-in capital	899,802	863,558
Retained earnings	2,630,867	2,548,542
Accumulated other comprehensive income	15,716	21,767
Treasury stock, at cost, 39,105,426 shares and 38,146,738 shares at June 30, 2013 and December 31, 2012, respectively	(817,409)	(795,051)
Total stockholders' equity	2,730,840	2,640,657
Total liabilities and stockholders' equity	$ 4,663,716	$ 4,556,911