REGULATORY ACTIONS, Deferred Energy (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Nevada Deferred Energy
Nevada Deferred Energy Balance at period end	$ (71,329)
Amortization	55,053
Cumulative balance as filed	(151,880)
Deferred Energy Under Collection	25,498	[1]
Reinstatement of deferred energy (effective 6/07, 10 years)	99,113
Total Deferred Energy	27,784
Deferred Assets
Deferred energy	84,120		87,072
Current Liabilities
Deferred energy	56,336		136,865
NPC Electric [Member]
Nevada Deferred Energy
Nevada Deferred Energy Balance at period end	(53,908)
Amortization	30,313
Cumulative balance as filed	(101,117)
Deferred Energy Under Collection	16,896	[1]
Reinstatement of deferred energy (effective 6/07, 10 years)	99,113
Total Deferred Energy	45,205
Deferred Assets
Deferred energy	84,120
Current Liabilities
Deferred energy	(38,915)
SPPC Electric [Member]
Nevada Deferred Energy
Nevada Deferred Energy Balance at period end	(13,602)
Amortization	11,296
Cumulative balance as filed	(32,693)
Deferred Energy Under Collection	7,795	[1]
Reinstatement of deferred energy (effective 6/07, 10 years)	0
Total Deferred Energy	(13,602)
Current Liabilities
Deferred energy	(13,602)
SPPC Gas [Member]
Nevada Deferred Energy
Nevada Deferred Energy Balance at period end	(3,819)
Amortization	13,444
Cumulative balance as filed	(18,070)
Deferred Energy Under Collection	807	[1]
Reinstatement of deferred energy (effective 6/07, 10 years)	0
Total Deferred Energy	(3,819)
Current Liabilities
Deferred energy	$ (3,819)

[1] These deferred energy under collections are subject to quarterly rate resets as discussed in Note 1, Summary of Significant AccountingPolicies, Deferred Energy Accounting, of the Notes to Financial Statements in the 2012 Form 10-K.