Goodwill (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Jun. 30, 2014 Public Service Company of New Mexico [Member]	Apr. 01, 2014 Public Service Company of New Mexico [Member]	Dec. 31, 2013 Public Service Company of New Mexico [Member]	Apr. 01, 2013 Public Service Company of New Mexico [Member]	Jun. 30, 2014 Texas-New Mexico Power Company [Member]	Dec. 31, 2013 Texas-New Mexico Power Company [Member]	Apr. 01, 2012 Texas-New Mexico Power Company [Member]
Goodwill [Line Items]
Goodwill	$ 278,297	$ 278,297	$ 278,297	$ 51,632	$ 51,600	$ 51,632		$ 226,665	$ 226,665	$ 226,700
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount					30.00%		27.00%			26.00%