Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Current federal income tax	$ 60	$ 0	$ 0
Current state income tax	43	(244)	(188)
Deferred federal income tax	(20,372)	7,716	119,182
Deferred state income tax	(4,491)	648	11,632
Amortization of accumulated investment tax credits	(522)	(345)	(286)
Total income taxes (benefit)	(25,282)	7,775	130,340
Public Service Company of New Mexico
Income Taxes [Line Items]
Current federal income tax	(6,266)	(6,644)	118
Current state income tax	449	(2,661)	(1,112)
Deferred federal income tax	(12,308)	5,661	73,308
Deferred state income tax	(7,590)	(2,080)	9,527
Amortization of accumulated investment tax credits	(247)	(247)	(286)
Total income taxes (benefit)	(25,962)	(5,971)	81,555
Texas-New Mexico Power Company
Income Taxes [Line Items]
Current federal income tax	10,792	13,347	2,472
Current state income tax	1,904	1,753	1,765
Deferred federal income tax	(7,621)	(540)	27,304
Deferred state income tax	(29)	2,320	(29)
Total income taxes (benefit)	$ 5,046	$ 16,880	$ 31,512