Fair Value of Derivative and Other Financial Instruments - Maturities of Securities (Details) $ in Thousands	Dec. 31, 2016 USD ($)
PNMR and PNM [Member]
Available-for-Sale
Within 1 year	$ 4,291
After 1 year through 5 years	35,884
After 5 years through 10 years	52,651
After 10 years through 15 years	5,617
After 15 years through 20 years	6,924
After 20 years	34,055
Available-for-sale debt securities	139,422
PNM Resources [Member]
Held-to-Maturity
Within 1 year	0
After 1 year through 5 years	100,893
After 5 years through 10 years	0
After 10 years through 15 years	0
After 15 years through 20 years	0
After 20 years	0
Held-to-maturity debt securities	$ 100,893