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Pension and Other Postretirement Benefits - Actuarial (Gain) Loss Results (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Public Service Company of New Mexico | Pension Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Discount rates | $ 27,547 | $ 41,849
Claims, contributions, and demographic experience | (1,249) | (334)
Other assumption and experience | 0 | (2,052)
Actuarial (gain) loss | 26,298 | 39,463
Public Service Company of New Mexico | Other Postretirement Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Discount rates | 3,536 | 6,569
Claims, contributions, and demographic experience | (5,845) | 19,562
Assumed participation rate | 0 | (6,335)
Mortality rate | 0 | (691)
Medical benefits | 1,425 | (1,228)
Dental trend assumption | (717) | 0
Actuarial (gain) loss | (1,601) | 17,877
Texas-New Mexico Power Company | Pension Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Discount rates | 3,528 | 5,055
Claims, contributions, and demographic experience | (517) | (556)
Other assumption and experience | 39 | (181)
Actuarial (gain) loss | 3,050 | 4,318
Texas-New Mexico Power Company | Other Postretirement Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Discount rates | 613 | 1,112
Claims, contributions, and demographic experience | (994) | (102)
Assumed participation rate | 0 | (1,013)
Mortality rate | 0 | (93)
Medical benefits | 0 | 0
Dental trend assumption | 0 | 0
Actuarial (gain) loss | $ (381) | $ (96)

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- Definition Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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