Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 2,145,398	$ 1,756,427	$ 2,108,474	$ 1,741,750
Total Other Comprehensive Income (Loss)	(1,267)	2,705	(1,437)	9,501
Ending balance	2,201,364	1,832,595	2,201,364	1,832,595
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(79,353)	(92,581)	(79,183)	(99,377)
Amounts reclassified from AOCI (pre-tax)			(2,762)	(2,048)
Income tax impact of amounts reclassified			701	521
Other OCI changes (pre-tax)			836	14,783
Income tax impact of other OCI changes			(212)	(3,755)
Total Other Comprehensive Income (Loss)	(1,267)	2,705	(1,437)	9,501
Ending balance	(80,620)	(89,876)	(80,620)	(89,876)
Fair Value Adjustment for Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(672)	(322)
Amounts reclassified from AOCI (pre-tax)			(903)	(1,117)
Income tax impact of amounts reclassified			229	284
Other OCI changes (pre-tax)			1,804	33
Income tax impact of other OCI changes			(458)	(9)
Total Other Comprehensive Income (Loss)			672	(809)
Ending balance	0	(1,131)	0	(1,131)
PNM
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,920,956	1,506,198	1,863,752	1,512,431
Total Other Comprehensive Income (Loss)	(1,267)	2,247	(2,109)	10,310
Ending balance	1,945,851	1,607,116	1,945,851	1,607,116
PNM | Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(79,353)	(90,992)	(78,511)	(99,055)
Amounts reclassified from AOCI (pre-tax)			(1,859)	(931)
Income tax impact of amounts reclassified			472	237
Other OCI changes (pre-tax)			(968)	14,750
Income tax impact of other OCI changes			246	(3,746)
Total Other Comprehensive Income (Loss)	(1,267)	2,247	(2,109)	10,310
Ending balance	(80,620)	(88,745)	(80,620)	(88,745)
PNM | Unrealized Gains on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			20,403	10,638
Amounts reclassified from AOCI (pre-tax)			(8,120)	(7,156)
Income tax impact of amounts reclassified			2,062	1,818
Other OCI changes (pre-tax)			(968)	14,750
Income tax impact of other OCI changes			246	(3,746)
Total Other Comprehensive Income (Loss)			(6,780)	5,666
Ending balance	13,623	16,304	13,623	16,304
PNM | Pension Liability Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(98,914)	(109,693)
Amounts reclassified from AOCI (pre-tax)			6,261	6,225
Income tax impact of amounts reclassified			(1,590)	(1,581)
Other OCI changes (pre-tax)			0	0
Income tax impact of other OCI changes			0	0
Total Other Comprehensive Income (Loss)			4,671	4,644
Ending balance	$ (94,243)	$ (105,049)	$ (94,243)	$ (105,049)