Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 1,756,427	$ 1,674,740	$ 1,741,750	$ 1,752,594
Total Other Comprehensive Income	2,705	1,301	9,501	9,803
Ending balance	1,832,595	1,735,088	1,832,595	1,735,088
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(92,581)	(100,182)	(99,377)	(108,684)
Amounts reclassified from AOCI (pre-tax)			(2,048)	(6,303)
Income tax impact of amounts reclassified			521	1,602
Other OCI changes (pre-tax)			14,783	19,442
Income tax impact of other OCI changes			(3,755)	(4,938)
Total Other Comprehensive Income	2,705	1,301	9,501	9,803
Ending balance	(89,876)	(98,881)	(89,876)	(98,881)
Fair Value Adjustment for Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(322)	1,738
Amounts reclassified from AOCI (pre-tax)			(1,117)	707
Income tax impact of amounts reclassified			284	(179)
Other OCI changes (pre-tax)			33	(3,664)
Income tax impact of other OCI changes			(9)	931
Total Other Comprehensive Income			(809)	(2,205)
Ending balance	(1,131)	(467)	(1,131)	(467)
PNM
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,506,198	1,402,493	1,512,431	1,461,571
Total Other Comprehensive Income	2,247	1,534	10,310	12,008
Ending balance	1,607,116	1,486,339	1,607,116	1,486,339
PNM | Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(90,992)	(99,948)	(99,055)	(110,422)
Amounts reclassified from AOCI (pre-tax)			(931)	(7,010)
Income tax impact of amounts reclassified			237	1,781
Other OCI changes (pre-tax)			14,750	23,106
Income tax impact of other OCI changes			(3,746)	(5,869)
Total Other Comprehensive Income	2,247	1,534	10,310	12,008
Ending balance	(88,745)	(98,414)	(88,745)	(98,414)
PNM | Unrealized Gains on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			10,638	1,939
Amounts reclassified from AOCI (pre-tax)			(7,156)	(12,563)
Income tax impact of amounts reclassified			1,818	3,191
Other OCI changes (pre-tax)			14,750	23,106
Income tax impact of other OCI changes			(3,746)	(5,869)
Total Other Comprehensive Income			5,666	7,865
Ending balance	16,304	9,804	16,304	9,804
PNM | Pension Liability Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(109,693)	(112,361)
Amounts reclassified from AOCI (pre-tax)			6,225	5,553
Income tax impact of amounts reclassified			(1,581)	(1,410)
Total Other Comprehensive Income			4,644	4,143
Ending balance	$ (105,049)	$ (108,218)	$ (105,049)	$ (108,218)