Pension and Other Postretirement Benefits APBO, PBO, Fair Value of Plan Assets, and Funded Status of the Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Non-current liability	$ 73,097	$ 110,738
Public Service Company of New Mexico [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Non-current liability	66,285	102,850
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning balance	657,557	599,537
Service cost	0	0	$ 0
Interest cost	28,255	30,163	28,142
Actuarial (gain) loss	(38,151)	72,524
Benefits paid	(49,761)	(44,667)
Ending balance	597,900	657,557	599,537
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	587,909	556,353
Actual return on plan assets	(10,225)	76,223
Employer contributions	30,000	0
Benefits paid	(49,761)	(44,667)
Fair value of plan assets at end of year	557,923	587,909	556,353
Funded status – asset (liability) for pension benefits	(39,977)	(69,648)
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning balance	95,175	92,165
Service cost	204	181	260
Interest cost	4,089	4,630	4,113
Participant contributions	2,439	2,582
Actuarial (gain) loss	(6,565)	4,455
Benefits paid	(10,668)	(8,838)
Ending balance	84,674	95,175	92,165
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	78,175	73,565
Actual return on plan assets	(617)	7,334
Employer contributions	3,623	3,532
Participant contributions	2,439	2,582
Benefits paid	(10,668)	(8,838)
Fair value of plan assets at end of year	72,952	78,175	73,565
Funded status – asset (liability) for pension benefits	(11,722)	(17,000)
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning balance	17,730	16,363
Service cost	0	0	0
Interest cost	760	822	720
Actuarial (gain) loss	(908)	2,040
Benefits paid	(1,477)	(1,495)
Ending balance	16,105	17,730	16,363
Less current liability	1,519	1,528
Non-current liability	14,586	16,202
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefits paid	(1,477)	(1,495)
Texas-New Mexico Power Company [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Non-current liability	6,812	7,888
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning balance	72,305	66,159
Service cost	0	0	0
Interest cost	3,043	3,193	3,087
Actuarial (gain) loss	(5,157)	8,466
Benefits paid	(5,993)	(5,513)
Ending balance	64,198	72,305	66,159
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	69,177	66,118
Actual return on plan assets	(1,102)	8,572
Employer contributions	0	0
Benefits paid	(5,993)	(5,513)
Fair value of plan assets at end of year	62,082	69,177	66,118
Funded status – asset (liability) for pension benefits	(2,116)	(3,128)
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning balance	14,070	12,266
Service cost	247	237	299
Interest cost	608	619	566
Participant contributions	320	366
Actuarial (gain) loss	(575)	1,639
Benefits paid	(1,564)	(1,057)
Ending balance	13,106	14,070	12,266
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	10,094	9,601
Actual return on plan assets	(82)	841
Employer contributions	343	343
Participant contributions	320	366
Benefits paid	(1,564)	(1,057)
Fair value of plan assets at end of year	9,111	10,094	9,601
Funded status – asset (liability) for pension benefits	(3,995)	(3,976)
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Beginning balance	878	823
Service cost	0	0	0
Interest cost	36	39	36
Actuarial (gain) loss	(26)	110
Benefits paid	(94)	(94)
Ending balance	794	878	$ 823
Less current liability	93	94
Non-current liability	701	784
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefits paid	$ (94)	$ (94)