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Summary of Business and Significant Accounting Policies (Inventories/Depreciation and Amortization) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Public Utilities, Inventory [Line Items] |  |  |
Inventory, Net | 59,643 | 54,231 |
Coal [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory, Net | 19,231 | 17,175 |
Materials and supplies [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory, Net | 40,412 | 37,056 |
Public Service Company of New Mexico [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory, Net | 56,790 | 51,521 |
Public Service Company of New Mexico [Member] | Coal [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory, Net | 19,231 | 17,175 |
Public Service Company of New Mexico [Member] | Materials and supplies [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory, Net | 37,559 | 34,346 |
Public Service Company of New Mexico [Member] | Electric plant [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Depreciation average rates used (as a percent) | 2.25% | 2.24% | 2.24%
Public Service Company of New Mexico [Member] | Common, intangible, and general plant [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Depreciation average rates used (as a percent) | 5.35% | 6.03% | 5.63%
Texas-New Mexico Power Company [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory, Net | 2,853 | 2,710 |
Depreciation average rates used (as a percent) | 3.56% | 3.41% | 3.39%
Texas-New Mexico Power Company [Member] | Coal [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory, Net | 0 | 0 |
Texas-New Mexico Power Company [Member] | Materials and supplies [Member] |  |  |
Public Utilities, Inventory [Line Items] |  |  |
Inventory, Net | 2,853 | 2,710 |

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- Definition Carrying amount (lower of cost or market) as of the balance sheet date of inventories less all valuation and other allowances. Excludes noncurrent inventory balances (expected to remain on hand past one year or one 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=6386567&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=6361293&loc=d3e6676-107765 + Details
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- Details
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- Definition Composite depreciation rate for public utility plants in service. + References No definition available. + Details
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