CONTINGENCIES - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011 LegalMatter
Securities Class Actions
Loss Contingencies [Line Items]
Number of lawsuits filed	3
Securities Class Actions First Lawsuit
Loss Contingencies [Line Items]
Lawsuit filing date	March 9, 2010
Securities Class Actions Second Lawsuit
Loss Contingencies [Line Items]
Lawsuit filing date	March 18, 2010
Securities Class Actions Third Lawsuit
Loss Contingencies [Line Items]
Lawsuit filing date	April 7, 2010
Stockholder Derivative Cases
Loss Contingencies [Line Items]
Number of lawsuits filed	4
Stockholder Derivative Cases For County Of Washoe
Loss Contingencies [Line Items]
Number of lawsuits filed	2
Descriptions of derivative cases filed	The two stockholder derivative cases filed in the Second Judicial District Court of the State of Nevada were consolidated by the Court in an order dated May 27, 2010
Descriptions of derivative cases filed by plaintiff	Filed a consolidated derivative complaint on September 7, 2010
Descriptions of derivative cases filed by defendant	In accordance with a stipulation between the parties, filed a motion to dismiss on November 16, 2010.
Stockholder Derivative Cases For District Of Nevada
Loss Contingencies [Line Items]
Number of lawsuits filed	2
Descriptions of derivative cases filed	The two federal derivative cases filed in the United States District Court were consolidated by the Court in an order dated August 31, 2010.
Descriptions of derivative cases filed by plaintiff	Filed a consolidated derivative complaint on October 28, 2010
Descriptions of derivative cases filed by defendant	In accordance with a stipulation by the parties, defendants intend to file a motion to dismiss by December 13, 2010.
Stockholder Derivative Cases For County Of Washoe First Lawsuit
Loss Contingencies [Line Items]
Lawsuit filing date	March 16, 2010
Stockholder Derivative Cases For County Of Washoe Second Lawsuit
Loss Contingencies [Line Items]
Lawsuit filing date	April 21, 2010
Stockholder Derivative Cases For District Of Nevada First Lawsuit
Loss Contingencies [Line Items]
Lawsuit filing date	March 29, 2010
Stockholder Derivative Cases For District Of Nevada Second Lawsuit
Loss Contingencies [Line Items]
Lawsuit filing date	June 7, 2010
Pending or Threatened Litigation
Loss Contingencies [Line Items]
Refund to customers equaling the time value of the revenues collected during the periods of non-compliance with FERC's requirements for QF status	1.6