XML 123 R92.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Stock-Based Compensation - Weighted Average Assumptions (Details) - $ / shares | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Restricted Shares and Performance-Based Shares |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Expected quarterly dividends per share (in dollars per share) | $ 0.2425 | $ 0.2200 | $ 0.2000
Risk-free interest rate | 1.50% | 0.94% | 0.92%
Market-Based Shares |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Dividend yield | 2.67% | 2.74% | 2.87%
Expected volatility | 20.80% | 20.44% | 18.73%
Risk-free interest rate | 1.54% | 0.97% | 1.00%

X
- Definition Share Based Compensation Arrangement by Share Based Payment Award Fair Value Assumptions Expected Quarterly Dividend Rate + References No definition available. + Details
Name: | pnm_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedQuarterlyDividendRate
Namespace Prefix: | pnm_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_AwardTypeAxis=pnm_RestrictedStockAndPerformanceSharesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=pnm_MarketBasedSharesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |