SEGMENT INFORMATION (Details) (USD $) In Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Segment Reporting Information [Line Items]
OPERATING REVENUES	$ 674,931	[1]	$ 782,683	[1]	$ 1,315,914	[1]	$ 1,497,172	[1]
Energy Costs:
Fuel for power generation	156,803		181,662		303,141		403,281
Purchased power	160,308		165,321		295,324		272,684
Gas purchased for resale	24,984		25,154		77,616		90,713
Deferred Energy	(8,106)		54,933		(10,058)		72,499
Total energy costs	333,989		427,070		666,023		839,177
Gross Margin	340,942		355,613	[1]	649,891	[1]	657,995	[1]
Other operating expenses	97,547		101,388		203,521		208,014
Maintenance	32,186		28,860		61,948		54,589
Depreciation and amortization	89,606		84,696		172,708		165,644
Taxes other than income	14,684		15,939		30,929		32,112
OPERATING INCOME	106,919		124,730		180,785		197,636
NPC Electric [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUES	473,898	[1]	539,395	[1]	863,966	[1]	965,194	[1]
Energy Costs:
Fuel for power generation	114,744		132,067		215,814		288,182
Purchased power	122,408		124,740		217,974		195,967
Deferred Energy	2,350		39,960		9,080		59,423
Total energy costs	239,502		296,767		442,868		543,572
Gross Margin	234,396		242,628	[1]	421,098	[1]	421,622	[1]
Other operating expenses	61,935		63,292		127,036		130,011
Maintenance	19,325		18,219		41,662		35,238
Depreciation and amortization	61,913		57,654		119,586		112,755
Taxes other than income	9,046		9,793		19,104		19,819
OPERATING INCOME	82,177		93,670		113,710		123,799
SPPC Electric [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUES	164,582	[1]	202,877	[1]	343,199	[1]	411,539	[1]
Energy Costs:
Fuel for power generation	42,059		49,595		87,327		115,099
Purchased power	37,900		40,581		77,350		76,717
Deferred Energy	(11,898)		8,725		(23,829)		7,225
Total energy costs	68,061		98,901		140,848		199,041
Gross Margin	96,521		103,976	[1]	202,351	[1]	212,498	[1]
SPPC Gas [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUES	36,448		40,405		108,742		120,425
Energy Costs:
Gas purchased for resale	24,984		25,154		77,616		90,713
Deferred Energy	1,442		6,248		4,691		5,851
Total energy costs	26,426		31,402		82,307		96,564
Gross Margin	10,022		9,003		26,435		23,861
SPPC Total [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUES	201,030	[1]	243,282	[1]	451,941	[1]	531,964	[1]
Energy Costs:
Fuel for power generation	42,059		49,595		87,327		115,099
Purchased power	37,900		40,581		77,350		76,717
Gas purchased for resale	24,984		25,154		77,616		90,713
Deferred Energy	(10,456)		14,973		(19,138)		13,076
Total energy costs	94,487		130,303		223,155		295,605
Gross Margin	106,543		112,979	[1]	228,786	[1]	236,359	[1]
Other operating expenses	34,687		37,014		74,903		76,367
Maintenance	12,861		10,641		20,286		19,351
Depreciation and amortization	27,693		27,042		53,122		52,889
Taxes other than income	5,599		6,098		11,623		12,164
OPERATING INCOME	25,703		32,184		68,852		75,588
NVE Other
Segment Reporting Information [Line Items]
OPERATING REVENUES	3		6		7		14
Energy Costs:
Total energy costs	0		0		0		0
Gross Margin	3		6		7		14
Other operating expenses	925		1,082		1,582		1,636
Taxes other than income	39		48		202		129
OPERATING INCOME	$ (961)		$ (1,124)		$ (1,777)		$ (1,751)

[1] As reported in our 2010 Form 10-K, amounts for REPR are presented net. As such, revenues and gross margin for the three months ended June 30, 2010 were reduced by $2.7 million, $1.4 million and $1.3 million for NVE, NPC and SPPC, respectively, from that reported in Forms 10-Q/A for the period ended June 30, 2010. Revenues and gross margin for the six months ended June 30, 2010 were reduced by $5.2 million, $2.6 million and $2.6 million for NVE, NPC and SPPC, respectively, from that reported in Forms 10-Q/A for the period ended June 30, 2010. The change in presentation did not affect operating income or net income.