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

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

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

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Share based Compensation, weighted percentage assigned to achieving market targets

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Share based Compensation, weighted percentage assigned to achieving performance targets

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

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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

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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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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).

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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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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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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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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit 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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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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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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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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Number of shares authorized for issuance under share-based payment arrangement.

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

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

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

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

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

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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Stock-Based Compensation - Restricted Stock Awards (Details) - USD ($)			12 Months Ended
	Mar. 02, 2018	Mar. 03, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Feb. 28, 2018	Feb. 28, 2017	Dec. 31, 2015	Jan. 01, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Additional pre tax expense			$ 6,400,000	$ 7,100,000	$ 6,200,000
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, Options, Additional Disclosures [Abstract]
Number of shares authorized (in shares)						35,906		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, Options, Additional Disclosures [Abstract]
Number of shares authorized (in shares)						17,953
Executive Vice President and Chief Financial Officer \| Common Stock \| Achieved performance target for 2015 and 2016
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]
Number of shares approved upon meeting target (in shares)							100,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than 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, Options, Additional Disclosures [Abstract]
Value of stock to be granted if performance targets are achieved									$ 275,000
Restricted Stock
Restricted Stock, Shares
Beginning balance (in shares)			166,651
Granted (in shares)			134,573
Exercised (in shares)			(138,001)
Forfeited (in shares)			(1,681)
Expired (in shares)			0
Ending balance (in shares)			161,542	166,651
Restricted Stock, Weighted-Average Grant Date Fair Value
Beginning balance (in dollars per share)			$ 32.93
Granted (in dollars per share)			37.92	$ 29.65	$ 23.06
Exercised (in dollars per share)			31.44
Forfeited (in dollars per share)			39.61
Expired (in dollars per share)			0
Ending balance (in dollars per share)			$ 38.21	32.93
Stock Options, Shares
Expired (in shares)			0
Options, Weighted Average Exercise Price
Expired (in dollars per share)			$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Weighted-average grant date fair value (in dollars per share)			$ 37.92	$ 29.65	$ 23.06
Total fair value of restricted shares that vested			$ 6,246,000	$ 8,558,000	$ 5,747,000
Stock Options
Restricted Stock, Shares
Expired (in shares)			0
Restricted Stock, Weighted-Average Grant Date Fair Value
Expired (in dollars per share)			$ 0
Stock Options, Shares
Beginning balance (in shares)			81,000
Granted (in shares)			0
Exercised (in shares)			(79,000)
Forfeited (in shares)			0
Expired (in shares)			0
Ending balance (in shares)			2,000	81,000
Options, Weighted Average Exercise Price
Beginning balance (in dollars per share)			$ 11.94
Granted (in dollars per share)			0
Exercised (in dollars per share)			11.93
Forfeited (in dollars per share)			0
Expired (in dollars per share)			0
Ending balance (in dollars per share)			$ 12.22	$ 11.94
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Aggregate intrinsic value of stock options outstanding			$ 100,000
Exercise price of stock options that are greater than the closing price (in shares)			0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Total intrinsic value of options exercised			$ 2,617,000	$ 3,117,000	2,234,000
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Additional pre tax expense				1,000,000.0
Performance Shares \| Executive
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Shares excluded in year two (in shares)			150,543
Shares excluded in year three (in shares)			147,202
Performance period			3 years
Performance Shares \| Executive \| Achieved performance target for 2016 through 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Shares excluded (in shares)			47,279
Weighted percentage assigned to achieving market targets			40.00%
Weighted percentage assigned to achieving performance targets			60.00%
Performance Shares \| Executive \| Achieved performance target for 2017 through 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Shares excluded (in shares)			122,277
Public Service Company of New Mexico
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Additional pre tax expense			$ 4,200,000	4,900,000	4,400,000
Public Service Company of New Mexico \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Additional pre tax expense				700,000
Texas-New Mexico Power Company
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Additional pre tax expense			$ 2,200,000	2,200,000	$ 1,800,000
Texas-New Mexico Power Company \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Additional pre tax expense				$ 300,000