Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 1,741,750	$ 1,752,594
Total Other Comprehensive Income (Loss)	(4,050)	5,445
Ending balance	1,687,569	1,747,458
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(99,377)	(108,684)
Amounts reclassified from AOCI (pre-tax)	852	1,445
Income tax impact of amounts reclassified	(216)	(366)
Other OCI changes (pre-tax)	(6,281)	5,853
Income tax impact of other OCI changes	1,595	(1,487)
Total Other Comprehensive Income (Loss)	(4,050)	5,445
Ending balance	(103,427)	(103,239)
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)	(38)	270
Income tax impact of amounts reclassified	10	(68)
Other OCI changes (pre-tax)	(1,998)	(1,225)
Income tax impact of other OCI changes	507	311
Total Other Comprehensive Income (Loss)	(1,519)	(712)
Ending balance	(1,841)	1,026
PNM
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,512,431	1,461,571
Total Other Comprehensive Income (Loss)	(2,531)	6,157
Ending balance	1,450,484	1,485,307
PNM \| Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(99,055)	(110,422)
Amounts reclassified from AOCI (pre-tax)	890	1,175
Income tax impact of amounts reclassified	(226)	(298)
Other OCI changes (pre-tax)	(4,283)	7,078
Income tax impact of other OCI changes	1,088	(1,798)
Total Other Comprehensive Income (Loss)	(2,531)	6,157
Ending balance	(101,586)	(104,265)
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)	(1,185)	(676)
Income tax impact of amounts reclassified	301	172
Other OCI changes (pre-tax)	(4,283)	7,078
Income tax impact of other OCI changes	1,088	(1,798)
Total Other Comprehensive Income (Loss)	(4,079)	4,776
Ending balance	6,559	6,715
PNM \| Pension Liability Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(109,693)	(112,361)
Amounts reclassified from AOCI (pre-tax)	2,075	1,851
Income tax impact of amounts reclassified	(527)	(470)
Total Other Comprehensive Income (Loss)	1,548	1,381
Ending balance	$ (108,145)	$ (110,980)

Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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