Condensed Consolidated Statements of Operations (Unaudited) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Condensed Consolidated Statements of Operations [Abstract]
Revenues	$ 565,342	$ 435,353	$ 1,490,129	$ 1,224,720
Costs and expenses:
Cost of services (exclusive of items shown separately below)	301,065	232,308	806,280	661,276
Depreciation, depletion, amortization and accretion	64,875	56,805	187,552	162,152
General and administrative expenses	95,391	84,912	278,151	248,165
Gain on sale of businesses			8,558
Income (loss) from operations	104,011	61,328	226,704	153,127
Other income (expense):
Interest expense, net	(19,115)	(12,456)	(47,940)	(39,174)
Earnings from equity-method investments, net	8,198	3,030	13,724	9,185
Income before income taxes	93,094	51,902	192,488	123,138
Income taxes	33,514	18,685	69,296	44,330
Net income	$ 59,580	$ 33,217	$ 123,192	$ 78,808
Basic earnings per share	$ 0.75	$ 0.42	$ 1.55	$ 1.00
Diluted earnings per share	$ 0.73	$ 0.42	$ 1.52	$ 0.99
Weighted average common shares used in computing earnings per share:
Basic	79,836	78,797	79,537	78,683
Incremental common shares from stock-based compensation	1,418	925	1,588	890
Diluted	81,254	79,722	81,125	79,573