Revenue From Major Customers (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Southern California Edison Company
Revenue, Major Customer [Line Items]
Revenues	$ 121,049	[1]	$ 108,481	[1]	$ 87,017	[1]
Percentage of Revenues	27.70%	[1]	29.10%	[1]	21.10%	[1]
Hawaii Electric Light Company
Revenue, Major Customer [Line Items]
Revenues	46,432	[1]	32,194	[1]	25,979	[1]
Percentage of Revenues	10.60%	[1]	8.60%	[1]	6.30%	[1]
Sierra Pacific Power Company And Nevada Power Company
Revenue, Major Customer [Line Items]
Revenues	56,778	[1],[2]	55,877	[1],[2]	53,658	[1],[2]
Percentage of Revenues	13.00%	[1],[2]	15.00%	[1],[2]	13.00%	[1],[2]
NGP Blue Mountain I LLC
Revenue, Major Customer [Line Items]
Revenues					46,893	[3]
Percentage of Revenues					11.40%	[3]
Central American Bank for Economic Integration (Las Pailas Project)
Revenue, Major Customer [Line Items]
Revenues			$ 21,365	[3]	$ 44,073	[3]
Percentage of Revenues			5.70%	[3]	10.70%	[3]

[1] Revenues reported in Electricity Segment.

[2] Subsidiaries of NV Energy, Inc.

[3] Revenues reported in Products Segment.