Pension and Other Postretirement Benefit Plans Pension Benefit Payments are Expected to be Paid (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2012	$ 1,477
2013	1,460
2014	1,441
2015	1,418
2016	1,393
Years 2017 - 2021	6,462
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2012	6,708
2013	6,874
2014	7,138
2015	7,270
2016	7,520
Years 2017 - 2021	38,933
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2012	40,809
2013	41,759
2014	42,536
2015	43,183
2016	43,715
Years 2017 - 2021	222,072
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2012	91
2013	90
2014	89
2015	87
2016	85
Years 2017 - 2021	375
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2012	777
2013	780
2014	797
2015	799
2016	816
Years 2017 - 2021	4,157
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2012	6,690
2013	5,806
2014	6,236
2015	6,046
2016	5,690
Years 2017 - 2021	$ 25,715