Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss	$ 59,488	$ 82,386
Regulatory liabilities related to income taxes	145,087	158,416
Federal tax credit carryforwards	101,231	76,481
Shutdown of SJGS Units 2 and 3	0	1,638
Regulatory disallowance related to NM 2015 Rate Case (Note 17)	34,639	0
Other	54,199	97,515
Total deferred tax assets	394,644	416,436
Deferred tax liabilities:
Depreciation and plant related	(787,928)	(767,482)
Investment tax credit	(81,186)	(57,853)
Regulatory assets related to income taxes	(58,495)	(62,889)
CTC	(1,466)	(3,613)
Pension	(35,029)	(35,407)
Regulatory asset for shutdown of SJGS Units 2 and 3	(28,831)	(30,425)
Other	(27,767)	(59,486)
Total deferred tax liabilities	(1,020,702)	(1,017,155)
Net accumulated deferred income tax liabilities	(626,058)	(600,719)
Public Service Company of New Mexico
Deferred tax assets:
Net operating loss	25,889	50,762
Regulatory liabilities related to income taxes	114,849	125,395
Federal tax credit carryforwards	82,983	62,230
Shutdown of SJGS Units 2 and 3	34,639	0
Regulatory disallowance related to NM 2015 Rate Case (Note 17)	0	1,638
Other	38,735	36,916
Total deferred tax assets	297,095	276,941
Deferred tax liabilities:
Depreciation and plant related	(630,293)	(606,673)
Investment tax credit	(74,667)	(55,484)
Regulatory assets related to income taxes	(49,479)	(53,561)
Pension	(30,609)	(31,046)
Regulatory asset for shutdown of SJGS Units 2 and 3	(28,831)	(30,425)
Other	(5,206)	(2,519)
Total deferred tax liabilities	(819,085)	(779,708)
Net accumulated deferred income tax liabilities	(521,990)	(502,767)
Texas-New Mexico Power Company
Deferred tax assets:
Regulatory liabilities related to income taxes	30,238	33,021
Other	3,788	4,517
Total deferred tax assets	34,026	37,538
Deferred tax liabilities:
Depreciation and plant related	(142,791)	(136,117)
Regulatory assets related to income taxes	(9,016)	(9,328)
Loss on reacquired debt	(6,345)	(6,617)
CTC	(1,466)	(3,613)
Pension	(4,420)	(4,361)
AMS	(8,473)	(10,030)
Other	(1,666)	(3,710)
Total deferred tax liabilities	(174,177)	(173,776)
Net accumulated deferred income tax liabilities	$ (140,151)	$ (136,238)