REGULATORY ACTIONS, Deferred Energy (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	$ (262,845)
Amortization	233,659
Deferred Energy Over Collections	(199,905)	[1]
Nevada Deferred Energy Balance	(229,091)
Reinstatement of deferred energy	105,154
Total Deferred Energy	(123,937)
Deferred Assets
Deferred energy	90,244		102,525
Current Liabilities
Deferred energy	214,181		245,164
NPC Electric [Member]
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	(177,336)
Amortization	148,747
Deferred Energy Over Collections	(126,504)	[1]
Nevada Deferred Energy Balance	(155,093)
Reinstatement of deferred energy	105,154
Total Deferred Energy	(49,939)
Deferred Assets
Deferred energy	90,244
Current Liabilities
Deferred energy	(140,183)
SPPC Electric [Member]
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	(56,422)
Amortization	65,038
Deferred Energy Over Collections	(53,440)	[1]
Nevada Deferred Energy Balance	(44,824)
Reinstatement of deferred energy	0
Total Deferred Energy	(44,824)
Current Liabilities
Deferred energy	(44,824)
SPPC Gas [Member]
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	(29,087)
Amortization	19,874
Deferred Energy Over Collections	(19,961)	[1]
Nevada Deferred Energy Balance	(29,174)
Reinstatement of deferred energy	0
Total Deferred Energy	(29,174)
Current Liabilities
Deferred energy	$ (29,174)

[1] These deferred energy over collections are subject to quarterly rate resets as discussed in Note 3, Regulatory Actions, of the Notes toFinancial Statements in the 2011 Form 10-K.