Condensed Consolidated Statements of Operations (Unaudited) (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Condensed Consolidated Statements of Operations [Abstract]
Revenues	$ 510,806	$ 424,856	$ 924,787	$ 789,367
Costs and expenses:
Cost of services (exclusive of items shown separately below)	271,370	229,916	505,215	428,968
Depreciation, depletion, amortization and accretion	63,314	54,299	122,677	105,347
General and administrative expenses	95,881	92,529	182,760	163,253
Gain on sale of businesses	5,884		8,558
Income from operations	86,125	48,112	122,693	91,799
Other income (expense):
Interest expense, net	(16,453)	(12,680)	(28,825)	(26,718)
Earnings from equity-method investments, net	5,499	2,170	5,526	6,155
Income before income taxes	75,171	37,602	99,394	71,236
Income taxes	27,062	13,537	35,782	25,645
Net income	$ 48,109	$ 24,065	$ 63,612	$ 45,591
Basic earnings per share	$ 0.60	$ 0.31	$ 0.80	$ 0.58
Diluted earnings per share	$ 0.59	$ 0.30	$ 0.79	$ 0.57
Weighted average common shares used in computing earnings per share:
Basic	79,744	78,716	79,385	78,625
Incremental common shares from stock-based compensation	1,510	885	1,639	874
Diluted	81,254	79,601	81,024	79,499