CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenues	$ 472,418	$ 502,235	$ 1,475,081	$ 1,327,025
Cost of revenues	271,401	279,936	826,479	724,179
Selling, general and administrative expenses	43,016	37,190	131,058	109,203
Depreciation and amortization	54,082	46,476	159,602	130,906
Loss on disposition of assets, net	1,551	4,179	4,859	2,690
Operating profit	102,368	134,454	353,083	360,047
Interest expense	(441)	(887)	(1,687)	(2,964)
Interest income	16	9	25	16
Other income (expense), net	1,104	(906)	1,144	(582)
Income before income taxes	103,047	132,670	352,565	356,517
Income tax provision	37,007	49,559	133,510	134,717
Net income	$ 66,040	$ 83,111	$ 219,055	$ 221,800
Earnings per share
Basic (in dollars per share)	$ 0.31	$ 0.38	$ 1.02	$ 1.02
Diluted (in dollars per share)	$ 0.30	$ 0.38	$ 1.01	$ 1.01
Dividends per share (in dollars per share)	$ 0.08	$ 0.05	$ 0.24	$ 0.15
Average shares outstanding
Basic (in shares)	215,151	217,910	215,211	217,752
Diluted (in shares)	216,645	220,299	216,819	220,433