Goodwill; Impairments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2008	Dec. 31, 2015	Apr. 01, 2015	Dec. 31, 2014	Apr. 01, 2014	Dec. 31, 2013	Apr. 01, 2012
Schedule of Goodwill and Other Intangible Assets [Line Items]
Goodwill		$ 278,297		$ 278,297		$ 278,297
Goodwill impairment	$ 174,400
Public Service Company of New Mexico [Member]
Schedule of Goodwill and Other Intangible Assets [Line Items]
Goodwill		51,632	$ 51,600	51,632	$ 51,600
Percentage of fair value in excess of carrying amount			25.00%		30.00%
Percentage increase in expected return on equity			0.50%		0.50%
Reduced percentage of fair value in excess of carrying value			18.00%		23.00%
Goodwill impairment	51,100
Texas-New Mexico Power Company [Member]
Schedule of Goodwill and Other Intangible Assets [Line Items]
Goodwill		$ 226,665	$ 226,700	$ 226,665	$ 226,700
Percentage of fair value in excess of carrying amount							26.00%
Goodwill impairment	$ 34,500