Discontinued Operations - Additional information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Jan. 31, 2010	Dec. 31, 2010
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
After-tax gain on sale of interest		$ 4,336,000
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		$ 4,300,000
Basic and diluted earnings (loss) per share		$ 0.10