Fair Value of Derivative and Other Financial Instruments - Non-Derivative Financial Instruments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Realized impairment loss	$ (1,200,000)	$ (4,300,000)	$ (700,000)
PNMR and PNM [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	272,977,000	259,042,000
Unrealized Gains	7,449,000	28,820,000
Proceeds from sales	522,601,000	252,174,000	117,989,000
Gross realized gains	46,116,000	29,663,000	15,162,000
Gross realized (losses)	(25,430,000)	(9,259,000)	$ (3,964,000)
Value of other than temporary impairments	0
PNMR and PNM [Member] | Cash and equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	23,683,000	10,700,000
Unrealized Gains	0	0
PNMR and PNM [Member] | Domestic value [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	34,796,000	44,505,000
Unrealized Gains	1,135,000	11,610,000
PNMR and PNM [Member] | Domestic growth [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	47,595,000	61,078,000
Unrealized Gains	3,032,000	11,163,000
PNMR and PNM [Member] | International and other [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	27,481,000	27,961,000
Unrealized Gains	2,029,000	1,569,000
PNMR and PNM [Member] | U.S. Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	40,962,000	27,880,000
Unrealized Gains	115,000	178,000
PNMR and PNM [Member] | Municipals [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	43,789,000	58,576,000
Unrealized Gains	585,000	3,672,000
PNMR and PNM [Member] | Corporate and other [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	54,671,000	28,342,000
Unrealized Gains	553,000	628,000
PNMR and PNM [Member] | Measured on a recurring basis [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	272,977,000	259,042,000
PNMR and PNM [Member] | Measured on a recurring basis [Member] | Nuclear Decommissioning Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	253,900,000	249,100,000
PNMR and PNM [Member] | Measured on a recurring basis [Member] | Mine Reclamation Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	19,100,000	9,900,000
PNMR and PNM [Member] | Measured on a recurring basis [Member] | Cash and equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	23,683,000	10,700,000
PNMR and PNM [Member] | Measured on a recurring basis [Member] | Domestic value [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	34,796,000	44,505,000
PNMR and PNM [Member] | Measured on a recurring basis [Member] | Domestic growth [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	47,595,000	61,078,000
PNMR and PNM [Member] | Measured on a recurring basis [Member] | International and other [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	27,481,000	27,961,000
PNMR and PNM [Member] | Measured on a recurring basis [Member] | U.S. Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	40,962,000	27,880,000
PNMR and PNM [Member] | Measured on a recurring basis [Member] | Municipals [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	43,789,000	58,576,000
PNMR and PNM [Member] | Measured on a recurring basis [Member] | Corporate and other [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 54,671,000	$ 28,342,000