Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 0	$ 0	$ 0
Interest cost	30,307	28,255	30,163
Expected return on plan assets	(35,416)	(39,323)	(38,044)
Amortization of net (gain) loss	13,820	14,820	13,020
Amortization of prior service cost	(965)	(965)	(965)
Net periodic benefit cost	7,746	2,787	4,174
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	140	204	181
Interest cost	4,346	4,089	4,630
Expected return on plan assets	(5,483)	(5,610)	(5,638)
Amortization of net (gain) loss	1,145	1,966	2,225
Amortization of prior service cost	(30)	(642)	(1,343)
Net periodic benefit cost	118	7	55
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	0
Interest cost	812	760	822
Amortization of net (gain) loss	256	325	210
Amortization of prior service cost	0	0	0
Net periodic benefit cost	1,068	1,085	1,032
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	0
Interest cost	3,304	3,043	3,193
Expected return on plan assets	(3,943)	(4,420)	(4,526)
Amortization of net (gain) loss	700	782	665
Amortization of prior service cost	0	0	0
Net periodic benefit cost	61	(595)	(668)
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	186	247	237
Interest cost	677	608	619
Expected return on plan assets	(490)	(520)	(534)
Amortization of net (gain) loss	(40)	0	(122)
Amortization of prior service cost	0	0	32
Net periodic benefit cost	333	335	232
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0	0	0
Interest cost	40	36	39
Amortization of net (gain) loss	2	5	0
Amortization of prior service cost	0	0	0
Net periodic benefit cost	$ 42	$ 41	$ 39