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DISCONTINUED OPERATIONS - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Jan. 31, 2010 Geothermal Development Limited	Sep. 30, 2010 Geothermal Development Limited	Sep. 30, 2010 Geothermal Development Limited
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Exercise of a call option to sale shares in GDL to a former shareholder					$ 2,800,000
Amount received to repay the loan provided by a subsidiary					17,700,000
Pre-tax gain on sale of interest							6,300,000
After-tax gain on sale of interest				4,336,000			4,300,000
Electricity revenues	$ 86,815,000	$ 83,357,000	$ 246,273,000	$ 218,269,000		$ 0	$ 64,000
Basic and diluted earnings per share				$ 0.10		$ 0.02	$ 0.10