Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Securities Class Actions LegalMatter	Dec. 31, 2012 Securities Class Actions First Lawsuit	Dec. 31, 2012 Securities Class Actions Second Lawsuit	Dec. 31, 2012 Securities Class Actions Third Lawsuit	Dec. 31, 2012 Stockholder Derivative Cases LegalMatter	Dec. 31, 2012 Stockholder Derivative Cases For County Of Washoe LegalMatter	Dec. 31, 2012 Stockholder Derivative Cases For District Of Nevada LegalMatter	Dec. 31, 2012 Stockholder Derivative Cases For County Of Washoe First Lawsuit	Dec. 31, 2012 Stockholder Derivative Cases For County Of Washoe Second Lawsuit	Dec. 31, 2012 Stockholder Derivative Cases For District Of Nevada First Lawsuit	Dec. 31, 2012 Stockholder Derivative Cases For District Of Nevada Second Lawsuit	Jan. 04, 2012 Specified Threshold North brawley MW	Jan. 04, 2012 Specified Threshold East Brawley Project MW	Dec. 31, 2012 Israel	Dec. 31, 2011 Israel	Dec. 31, 2012 Israel Minimum	Dec. 31, 2012 Israel Maximum	Dec. 31, 2012 Construction in Progress
Loss Contingencies [Line Items]
Royalty expense under geothermal resource agreements	$ 12,048,000	$ 10,138,000	$ 8,690,000
Letters of credit	217,800,000
Letters of credit fair value	0	0
Obligation related to supplier agreement	93,600,000																				42,500,000
Obligation related to supplier agreement payment year	2013
Required royalties payments as percentage of revenues																			3.50%	5.00%
Royalty payment cap amount																	1,500,000	1,400,000
Royalty payment cap increase based on LIBOR rate																	500,000
Number of lawsuits filed				3				4	2	2
Lawsuit filing date					2010-03-09	2010-03-18	2010-04-07				2010-03-16	2010-04-21	2010-03-29	2010-06-07
Cash payment to be funded by the company if the proposed class action dismissed	3,100,000
Descriptions of derivative cases filed									The two stockholder derivative cases filed in the Second Judicial District Court of the State of Nevada in and for the County of Washoe were consolidated by the Court in an order dated May 27, 2010.	The two stockholder derivative cases filed in the United States District Court for the District of Nevada were consolidated by the Court in an order dated August 31, 2010
Descriptions of derivative cases filed by plaintiff									Plaintiffs filed a consolidated derivative complaint on September 7, 2010.	Plaintiffs filed a consolidated derivative complaint on October 28, 2010.
Descriptions of derivative cases filed by defendant									In accordance with a stipulation between the parties, defendants filed a motion to dismiss on November 16, 2010.	The Company filed a motion to dismiss on December 13, 2010.
Corporate governance measures minimum	5 years
Attorneys fees	$ 700,000
Expected generating capacity															50	50