Pension and Other Postretirement Benefits - Actuarial (Gain) Loss Results (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Public Service Company of New Mexico | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rates	$ 66,108	$ (34,769)
Claims, contributions, and demographic experience	(732)	431
Mortality rate	(4,225)	(6,966)
Other assumptions and experience	0	279
Actuarial (gain) loss	61,151	(41,025)
Public Service Company of New Mexico | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rates	7,236	(4,076)
Claims, contributions, and demographic experience	(4,022)	(3,174)
Mortality rate	(627)	(916)
Assumed participation rate	0	(4,040)
Actuarial (gain) loss	2,587	(12,206)
Texas-New Mexico Power Company | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rates	8,006	(4,278)
Claims, contributions, and demographic experience	394	(301)
Mortality rate	(296)	(705)
Other assumptions and experience	(215)	68
Actuarial (gain) loss	7,889	(5,216)
Texas-New Mexico Power Company | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rates	1,375	(710)
Claims, contributions, and demographic experience	(311)	72
Mortality rate	(60)	(114)
Assumed participation rate	0	(1,461)
Actuarial (gain) loss	$ 1,004	$ (2,213)