Performance period

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- Definition

Share Based Compensation Arrangement by Share Based Payment Award Fair Value Assumptions Expected Quarterly Dividend Rate

+ References

No definition available.

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares in Year One

+ References

No definition available.

+ Details

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares in Year Three

+ References

No definition available.

+ Details

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares in Year Two

+ References

No definition available.

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- Definition

Share Based Compensation Arrangement by Share Based Payment Award Options Outstanding Shares Above Entities Stock Price

+ References

No definition available.

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- Definition

Share Based Compensation Arrangement by Share Based Payment Award Options Vested in Period Total Fair Value

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No definition available.

+ Details

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Vesting Rate

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No definition available.

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Previously Awarded Restricted Stock Exercised, Included in Shares Outstanding, Number

+ References

No definition available.

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Previously Awarded Restricted Stock Granted, Included in Shares Outstanding, Number

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No definition available.

+ Details

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- Definition

Share based Compensation, weighted percentage assigned to achieving market targets

+ References

No definition available.

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- Definition

Share based Compensation, weighted percentage assigned to achieving performance targets

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No definition available.

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- Definition

Share-based compensation arrangement by share-based payment award, Purchase price of common stock

+ References

No definition available.

+ Details

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- Definition

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

+ References

No definition available.

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- Definition

Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences with jurisdictional netting.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Unrecognized cost of unvested share-based compensation awards.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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-Subparagraph (c)(2)(iii)(1)
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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Section 50
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-Subparagraph (d)(2)
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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
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- References

No definition available.

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- 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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Subparagraph (f)(2)(iii)
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- 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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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.

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No definition available.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- References

No definition available.

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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

+ References

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- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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- Definition

Net number of share options (or share units) granted during the period.

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- Definition

Gross number of share options (or share units) granted during the period.

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No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

+ References

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- Definition

Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Stock-Based Compensation (Details) - USD ($)			3 Months Ended
Stock-Based Compensation (Details) - USD ($)	Mar. 02, 2018	Mar. 03, 2017	Mar. 31, 2018	Mar. 31, 2017	Feb. 28, 2018	Dec. 31, 2017	Feb. 28, 2017	Jan. 01, 2017	Mar. 31, 2015	Jan. 01, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted (in shares)			0
Vesting period			1 year
Unrecognized expense related to stock awards			$ 5,800,000			$ 3,800,000
Cumulative effect adjustment						(11,208,000)
Restricted Stock, Shares
Expired (in shares)			0
Restricted Stock, Weighted- Average Grant Date Fair Value
Expired (in dollars per share)			$ 0.00
Stock Options, Shares
Outstanding at beginning of period (in shares)			193,441
Granted (in shares)			0
Exercised (in shares)			(97,941)
Forfeited (in shares)			0
Expired (in shares)			0
Outstanding at end of period (in shares)			95,500
Stock Options, Weighted- Average Exercise Price
Outstanding at beginning of period (in dollars per share)			$ 9.98
Granted (in dollars per share)			0.00
Exercised (in dollars per share)			8.19
Forfeited (in dollars per share)			0.00
Expired (in dollars per share)			0.00
Outstanding at end of period (in dollars per share)			11.81
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average grant date fair value of options granted (in dollars per share)			$ 0.00	$ 0.00
Total fair value of options that vested			$ 0	$ 0
Total intrinsic value of options exercised			$ 2,711,000	$ 945,000
Chairman, President, and Chief Executive Officer \| Common Stock \| Achieves a specific performance target by the end of 2019 and she remains an employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares received if achieves specified improvement in total shareholders return (in shares)									53,859
Chairman, President, and Chief Executive Officer \| Common Stock \| Achieves a specific performance target by the end of 2017 and she remains an employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares received if achieves specified improvement in total shareholders return (in shares)									17,953
Executive Vice President and Chief Financial Officer \| Common Stock \| Achieved performance target for 2015 and 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of stock awarded										$ 100,000
Number of shares available for grant					275,000		100,000
Restricted Stock, Shares
Granted (in shares)	7,670	2,754
Restricted Stock, Weighted- Average Grant Date Fair Value
Granted (in dollars per share)	$ 35.85	$ 36.30
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average grant date fair value (in dollars per share)	$ 35.85	$ 36.30
Executive Vice President and Chief Financial Officer \| Common Stock \| Achieved performance target for 2015, 2016 and 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of stock awarded										$ 275,000
Retained Earnings
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative effect adjustment						11,208,000
Accounting Standards Update 2016-09
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accumulated deferred income taxes								$ (10,400,000)
PNM
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative effect adjustment						(11,208,000)
PNM \| Retained Earnings
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative effect adjustment						$ 11,208,000
Restricted Shares and Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of time stock expense is expected to be recognized			2 years 14 days	1 year 6 months 11 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected quarterly dividends per share (in dollars per share)			$ 0.2650	$ 0.2425
Risk-free interest rate			2.39%	1.58%
Restricted Stock
Restricted Stock, Shares
Outstanding at beginning of period (in shares)			189,045
Granted (in shares)			204,654
Exercised (in shares)			(201,162)
Forfeited (in shares)			(3,562)
Expired (in shares)			0
Outstanding at end of period (in shares)			188,975
Restricted Stock, Weighted- Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share)			$ 31.11
Granted (in dollars per share)			29.03	$ 22.12
Exercised (in dollars per share)			27.68
Forfeited (in dollars per share)			30.58
Expired (in dollars per share)			0.00
Outstanding at end of period (in dollars per share)			$ 32.52
Stock Options, Shares
Expired (in shares)			0
Stock Options, Weighted- Average Exercise Price
Expired (in dollars per share)			$ 0.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average grant date fair value (in dollars per share)			$ 29.03	$ 22.12
Total fair value of restricted shares that vested			$ 7,162,000	$ 5,024,000
Performance Shares \| Executive
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)			97,697
Shares exercised (in shares)			49,682
Weighted percentage assigned to achieving market targets			60.00%
Weighted percentage assigned to achieving performance targets			40.00%
Maximum number of shares awarded in year 1 (in shares)			134,219
Maximum number of shares awarded in year 2 (in shares)			155,291
Maximum number of shares awarded in year 3 (in shares)			152,750
Performance period			3 years
Market-Based Shares
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate			2.36%	1.54%
Dividend yield			2.96%	2.67%
Expected volatility			19.12%	20.80%
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of stock options outstanding			$ 2,500,000
Weighted-average remaining contract life			1 year 9 months 18 days
Number of outstanding stock options with an exercise price greater than the closing price (in shares)			0
Performance Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
Vesting rate			100.00%