Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 1,687,569	$ 1,747,458	$ 1,741,750	$ 1,752,594
Total Other Comprehensive Income	10,846	3,057	6,796	8,502
Ending balance	1,756,427	1,674,740	1,756,427	1,674,740
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(103,427)	(103,239)	(99,377)	(108,684)
Amounts reclassified from AOCI (pre-tax)			591	(1,374)
Income tax impact of amounts reclassified			(150)	350
Other OCI changes (pre-tax)			8,519	12,769
Income tax impact of other OCI changes			(2,164)	(3,243)
Total Other Comprehensive Income	10,846	3,057	6,796	8,502
Ending balance	(92,581)	(100,182)	(92,581)	(100,182)
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)			(500)	525
Income tax impact of amounts reclassified			127	(133)
Other OCI changes (pre-tax)			(1,198)	(3,169)
Income tax impact of other OCI changes			304	805
Total Other Comprehensive Income			(1,267)	(1,972)
Ending balance	(1,589)	(234)	(1,589)	(234)
PNM
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,450,484	1,485,307	1,512,431	1,461,571
Total Other Comprehensive Income	10,594	4,317	8,063	10,474
Ending balance	1,506,198	1,402,493	1,506,198	1,402,493
PNM | Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(101,586)	(104,265)	(99,055)	(110,422)
Amounts reclassified from AOCI (pre-tax)			1,091	(1,899)
Income tax impact of amounts reclassified			(277)	483
Other OCI changes (pre-tax)			9,717	15,938
Income tax impact of other OCI changes			(2,468)	(4,048)
Total Other Comprehensive Income	10,594	4,317	8,063	10,474
Ending balance	(90,992)	(99,948)	(90,992)	(99,948)
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)			(3,059)	(5,601)
Income tax impact of amounts reclassified			777	1,423
Other OCI changes (pre-tax)			9,717	15,938
Income tax impact of other OCI changes			(2,468)	(4,048)
Total Other Comprehensive Income			4,967	7,712
Ending balance	15,605	9,651	15,605	9,651
PNM | Pension Liability Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(109,693)	(112,361)
Amounts reclassified from AOCI (pre-tax)			4,150	3,702
Income tax impact of amounts reclassified			(1,054)	(940)
Total Other Comprehensive Income			3,096	2,762
Ending balance	$ (106,597)	$ (109,599)	$ (106,597)	$ (109,599)