REGULATORY ACTIONS, Deferred Energy (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	$ (260,079)
Amortization	148,481
Deferred Energy Over Collections	(148,448)	[1]
Nevada Deferred Energy Balance	(260,046)
Reinstatement of deferred energy	110,519
Total Deferred Energy	(149,527)
Deferred Assets
Deferred energy	95,599		102,525
Current Liabilities
Deferred energy	245,126		245,164
NPC Electric [Member]
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	(174,714)
Amortization	85,047
Deferred Energy Over Collections	(91,253)	[1]
Nevada Deferred Energy Balance	(180,920)
Reinstatement of deferred energy	110,519
Total Deferred Energy	(70,401)
Deferred Assets
Deferred energy	95,599
Current Liabilities
Deferred energy	(166,000)
SPPC Electric [Member]
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	(56,337)
Amortization	45,721
Deferred Energy Over Collections	(38,903)	[1]
Nevada Deferred Energy Balance	(49,519)
Reinstatement of deferred energy	0
Total Deferred Energy	(49,519)
Current Liabilities
Deferred energy	(49,519)
SPPC Gas [Member]
Nevada Deferred Energy
Deferred Energy Costs Authorized To Refund	(29,028)
Amortization	17,713
Deferred Energy Over Collections	(18,292)	[1]
Nevada Deferred Energy Balance	(29,607)
Reinstatement of deferred energy	0
Total Deferred Energy	(29,607)
Current Liabilities
Deferred energy	$ (29,607)

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