Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 204,636	$ 110,723
Accounts receivable, net of allowance for doubtful accounts of $3,681 and $3,513 at September 30, 2013 and December 31, 2012, respectively	488,804	465,517
Inventory	24,274	26,889
Deferred tax assets, net	29,179	52,959
Other	45,387	43,903
Total current assets	792,280	699,991
Property and equipment, net	3,651,574	3,615,383
Goodwill and intangible assets	168,380	171,463
Deposits on equipment purchases	41,027	43,776
Other	24,261	26,298
Total assets	4,677,522	4,556,911
Current liabilities:
Accounts payable	181,191	188,823
Federal and state income taxes payable	699	6,158
Accrued expenses	153,665	158,632
Current portion of long-term debt	10,000	6,250
Total current liabilities	345,555	359,863
Long-term debt	685,000	692,500
Deferred tax liabilities, net	896,655	857,302
Other	6,437	6,589
Total liabilities	1,933,647	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 186,515,121 and 184,059,900 issued and 144,251,523 and 145,913,162 outstanding at September 30, 2013 and December 31, 2012, respectively	1,865	1,841
Additional paid-in capital	906,639	863,558
Retained earnings	2,698,056	2,548,542
Accumulated other comprehensive income	18,099	21,767
Treasury stock, at cost, 42,263,598 shares and 38,146,738 shares at September 30, 2013 and December 31, 2012, respectively	(880,784)	(795,051)
Total stockholders' equity	2,743,875	2,640,657
Total liabilities and stockholders' equity	$ 4,677,522	$ 4,556,911