Pension and Other Postretirement Benefits - Actuarial (Gain) Loss Results (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rates	$ 41,849	$ (45,918)
Claims, contributions, and demographic experience	(334)	2,778
Other assumption and experience	(2,052)	4,989
Actuarial (gain) loss	39,463	(38,151)
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rates	6,569	(7,345)
Claims, contributions, and demographic experience	19,562	780
Assumed participation rate	(6,335)	0
Mortality rate	(691)	0
Medical benefits	(1,228)	0
Actuarial (gain) loss	17,877	(6,565)
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rates	5,055	(6,090)
Claims, contributions, and demographic experience	(556)	877
Other assumption and experience	(181)	56
Actuarial (gain) loss	4,318	(5,157)
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rates	1,112	(1,322)
Claims, contributions, and demographic experience	(102)	747
Assumed participation rate	(1,013)	0
Mortality rate	(93)	0
Medical benefits	0	0
Actuarial (gain) loss	$ (96)	$ (575)