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

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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, Vesting Rate

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

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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 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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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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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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Stock-Based Compensation - Narrative (Details) - USD ($) $ in Millions					12 Months Ended
	Sep. 16, 2024	May 03, 2024	Apr. 08, 2024	Dec. 04, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 04, 2024	May 31, 2023	May 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense for stock-based arrangements					$ 9.5	$ 7.2	$ 7.9
Conversion of equity based awards to common stock								1
Restricted Shares and Performance-Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense					$ 5.0
Period to recognize compensation expense					2 years 3 months 3 days
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested (in shares)					241,237	212,080
Granted (in shares)					249,282
Vested (in shares)					218,403
PNM
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense for stock-based arrangements					$ 5.0	$ 4.8	5.3
TNMP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense for stock-based arrangements					$ 2.7	$ 2.4	$ 2.6
Executive \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares excluded in year two (in shares)					150,976
Shares excluded in year three (in shares)					227,472
Performance period					3 years
Executive \| Performance Shares \| Achieved Performance Target for 2021 Through 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares excluded (in shares)					80,492
Executive \| Performance Shares \| Achieved Performance Target for 2022 Through 2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares excluded (in shares)					49,489
Executive \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested at one-time sign-on (in shares)					8,791
President And Chief Operating Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Retention bonus				$ 1.0
President And Chief Operating Officer \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of restricted shares that vested			$ 0.8
Granted (in shares)		19,851
Vested (in shares)		6,617
General Counsel, Senior Vice President Regulatory and Public Policy, and Corporate Secretary \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	9,300
General Counsel, Senior Vice President Regulatory and Public Policy, and Corporate Secretary \| Restricted Stock \| Share-Based Payment Arrangement, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%
General Counsel, Senior Vice President Regulatory and Public Policy, and Corporate Secretary \| Restricted Stock \| Share-Based Payment Arrangement, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%
Performance Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for awards					3 years
Vesting rate (as a percent)					100.00%
Number of shares authorized (in shares)									2,500,000	13,500,000
Charge to share pool for each share awarded					5
Performance Equity Plan \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for awards					3 years
Performance Equity Plan \| Nonemployee Members of the Board of Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for awards					1 year
Retention Agreement \| Restricted Stock \| Share-Based Payment Arrangement, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for awards				24 months
Retention Agreement \| Restricted Stock \| Share-Based Payment Arrangement, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for awards				6 months
Retention Agreement \| Chairman And Chief Executive Officer \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested (in shares)				26,766
Retention Agreement \| Senior Vice President And General Counsel \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested (in shares)				8,922