Fair Value of Derivative and Other Financial Instruments - Available for Sale Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Other than temporary impairment losses, Investments, portion recognized in earnings, net, available-for-sale securities	$ (2,400)	$ (1,200)	$ (3,200)	$ (700)
PNMR and PNM [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	242,795		242,795		$ 250,145
Unrealized Gains	26,720		26,720		46,348
Proceeds from sales	71,576	29,103	166,097	82,222
Gross realized gains	8,998	3,134	22,463	11,616
Gross realized (losses)	(4,014)	$ (936)	(7,133)	$ (2,731)
PNMR and PNM [Member] | Cash and equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	28,813		28,813		8,276
Unrealized Gains	0		0		0
PNMR and PNM [Member] | Domestic value [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	42,769		42,769		45,340
Unrealized Gains	11,880		11,880		17,418
PNMR and PNM [Member] | Domestic growth [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	58,424		58,424		74,053
Unrealized Gains	10,124		10,124		21,354
PNMR and PNM [Member] | International and other [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,681		1,681		16,599
Unrealized Gains	1		1		156
PNMR and PNM [Member] | U.S. Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	25,544		25,544		22,563
Unrealized Gains	598		598		903
PNMR and PNM [Member] | Municipals [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	61,106		61,106		68,973
Unrealized Gains	3,499		3,499		5,851
PNMR and PNM [Member] | Corporate and other [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	24,458		24,458		14,341
Unrealized Gains	618		618		666
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	242,795		242,795		250,145
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | Nuclear Decommissioning Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	237,300		237,300		244,600
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | Mine Reclamation Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	5,500		5,500		5,500
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | Cash and equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	28,813		28,813		8,276
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | Domestic value [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	42,769		42,769		45,340
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | Domestic growth [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	58,424		58,424		74,053
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | International and other [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,681		1,681		16,599
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | U.S. Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	25,544		25,544		22,563
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | Municipals [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	61,106		61,106		68,973
Fair Value, Measurements, Recurring [Member] | PNMR and PNM [Member] | Corporate and other [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 24,458		$ 24,458		$ 14,341