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Pension and Other Postretirement Benefits - Other Postretirement Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
401(k) plan
Defined Contribution Plan [Abstract]
401(k) plan	$ 16,452	$ 17,762	$ 16,725
401(k) plan | Public Service Company of New Mexico
Defined Contribution Plan [Abstract]
401(k) plan	12,120	13,397	12,679
401(k) plan | Texas-New Mexico Power Company
Defined Contribution Plan [Abstract]
401(k) plan	4,332	4,365	4,046
Non-qualified plan
Defined Contribution Plan [Abstract]
Non-qualified plan	3,702	2,017	1,436
Non-qualified plan | Public Service Company of New Mexico
Defined Contribution Plan [Abstract]
Non-qualified plan	2,834	1,535	1,090
Non-qualified plan | Texas-New Mexico Power Company
Defined Contribution Plan [Abstract]
Non-qualified plan	$ 868	$ 482	$ 346

X

- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

+ Details

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Balance Type:	debit
Period Type:	duration

X

- References

No definition available.

+ Details

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X

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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X

- Details

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X

- Details

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