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Significant Accounting Policies and Responsibility for Financial Statements (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Sep. 30, 2017 | Jul. 31, 2017 | Sep. 30, 2016 | Jul. 31, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Accounting Policies [Abstract] |  |  |  |  |  |  |  |
Payment defaults under agreements | $ 0 |  |  |  | $ 0 |  | $ 0 |
Unrealized gains, net of income taxes, recorded in AOCI | $ 9,800,000 |  |  |  | $ 9,800,000 |  | $ 9,800,000 |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |
Declared dividends on common stock (dollars per share) | $ 0.2425 | $ 0.2425 | $ 0.22 | $ 0.22 | $ 0.2425 | $ 0.22 | $ 0.7275 | $ 0.66
Dividends declared and paid |  |  |  |  |  |  | $ 57,948,000 |
PNM |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |
Equity contribution |  |  |  |  |  |  |  | $ 28,100,000
Dividends declared and paid |  |  |  |  |  |  |  | 4,100,000
Texas-New Mexico Power Company |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |
Equity contribution |  |  |  |  |  |  |  | 50,000,000
Dividends declared and paid |  |  |  |  |  |  | $ 29,663,000 | $ 18,000,000

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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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