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

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant