Related Party Transactions (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Electricity, transmission and distribution related services [Member] | TNMP to PNMR [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	$ 33,813,000		$ 39,084,000		$ 41,338,000
Service billings [Member] | PNM to TNMP [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	550,000		400,000		698,000
Service billings [Member] | TNMP to PNMR [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	164,000		319,000		636,000
Service billings [Member] | PNMR to PNM [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	98,914,000	[1]	93,602,000	[1]	80,141,000	[1]
Shared service billings					900,000
Service billings [Member] | PNMR to TNMP
Related Party Transaction [Line Items]
Amount of related party transaction	29,353,000		25,455,000		22,919,000
Service billings [Member] | PNMR to Optim Energy [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	4,083,000		5,778,000		6,743,000
Service billings [Member] | Optim Energy to PNMR [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	23,000		173,000		305,000
Income tax sharing payments [Member] | TNMP to PNMR [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	0		0		4,322,000
Income tax sharing payments [Member] | PNM to PNMR [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	0		0		126,527,000
Income tax sharing payments [Member] | PNMR to PNM [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	0		(59,298,000)		0
Income tax sharing payments [Member] | PNMR to TNMP
Related Party Transaction [Line Items]
Amount of related party transaction	0		(13,869,000)		0
Interest charges [Member] | TNMP to PNMR [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	40,000		281,000		849,000
Interest charges [Member] | PNM to PNMR [Member]
Related Party Transaction [Line Items]
Amount of related party transaction	$ 54,000		$ 13,000		$ 8,000

[1] of PNMR, PNM and TNMP: Year Ended December 31, 2011 2010 2009 (In thousands) Electricity, transmission and distribution related services billings: TNMP to PNMR$33,813 $39,084 $41,338Services billings: PNMR to PNM(1)98,914 93,602 80,141PNMR to TNMP29,353 25,455 22,919PNM to TNMP550 400 698TNMP to PNMR164 319 636PNMR to Optim Energy4,083 5,778 6,743Optim Energy to PNMR23 173 305Income tax sharing payments: PNM to PNMR— — 126,527TNMP to PNMR— — 4,322PNMR to TNMP— (13,869) —PNMR to PNM— (59,298) —Interest payments: PNM to PNMR54 13 8TNMP to PNMR40 281 849(1) Includes billings to PNM Gas of $0.9 million in 2009.