Pension and Other Postretirement Benefit Plans Pension Benefit Payments are Expected to be Paid (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	$ 1,452
2014	1,436
2015	1,418
2016	1,396
2017	1,371
Years 2018 - 2022	6,340
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	6,123
2014	6,327
2015	6,450
2016	6,668
2017	6,780
Years 2018 - 2022	34,983
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	42,186
2014	42,979
2015	43,573
2016	44,092
2017	44,608
Years 2018 - 2022	223,777
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	92
2014	91
2015	89
2016	87
2017	85
Years 2018 - 2022	371
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	786
2014	796
2015	803
2016	823
2017	838
Years 2018 - 2022	4,322
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2013	5,922
2014	6,189
2015	6,385
2016	5,982
2017	5,893
Years 2018 - 2022	$ 26,193