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Summary of the Business and Significant Accounting Policies - Inventories/Depreciation and Amortization (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Public Utilities, Inventory [Line Items] |  |  |
Inventory | $ 73,027 | $ 67,386 |
Coal [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory | 19,940 | 18,356 |
Materials and supplies [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory | 53,087 | 49,030 |
Public Service Company of New Mexico [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory | 64,401 | 60,477 |
Public Service Company of New Mexico [Member] | Coal [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory | 19,940 | 18,356 |
Public Service Company of New Mexico [Member] | Materials and supplies [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory | $ 44,461 | $ 42,121 |
Public Service Company of New Mexico [Member] | Electric plant [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Depreciation average rates used | 2.33% | 2.27% | 2.26%
Public Service Company of New Mexico [Member] | Common, intangible, and general plant [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Depreciation average rates used | 5.40% | 4.66% | 4.64%
Texas-New Mexico Power Company [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Depreciation average rates used | 3.66% | 3.65% | 3.59%
Inventory | $ 8,626 | $ 6,909 |
Texas-New Mexico Power Company [Member] | Coal [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory | 0 | 0 |
Texas-New Mexico Power Company [Member] | Materials and supplies [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory | $ 8,626 | $ 6,909 |

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- Definition Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 330 -SubTopic 10 -Section 35 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=68049868&loc=d3e3927-108312 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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