Income Taxes - Schedule of Deferred Income Tax Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Net change in deferred income tax liability per above table	$ (393,440)
Change in tax effects of income tax related regulatory assets and liabilities	(16,444)
Tax effect of mark-to-market adjustments	(4,724)
Tax effect of excess pension liability	(3,421)
Adjustment for uncertain income tax positions	2,677
Reclassification of unrecognized tax benefits	(2,677)
Regulatory recovery of prior year impairments of state net operating loss carryforward, net of amortization	(2,225)
Federal income tax rate change	548,952
Cumulative effect adjustment for excess tax benefit related to stock compensation awards	10,382
Alternative minimum tax carryforward reclassified to receivable	(8,336)
Other	(216)
Deferred income taxes	130,528	$ 63,805	$ 16,451
Public Service Company of New Mexico
Income Taxes [Line Items]
Net change in deferred income tax liability per above table	(299,654)
Change in tax effects of income tax related regulatory assets and liabilities	(16,332)
Tax effect of mark-to-market adjustments	(4,110)
Tax effect of excess pension liability	(3,421)
Adjustment for uncertain income tax positions	2,614
Reclassification of unrecognized tax benefits	(2,614)
Regulatory recovery of prior year impairments of state net operating loss carryforward, net of amortization	(2,225)
Federal income tax rate change	402,501
Cumulative effect adjustment for excess tax benefit related to stock compensation awards	7,770
Other	(1,980)
Deferred income taxes	82,549	53,119	(2,836)
Texas-New Mexico Power Company
Income Taxes [Line Items]
Net change in deferred income tax liability per above table	(119,370)
Change in tax effects of income tax related regulatory assets and liabilities	(112)
Federal income tax rate change	146,451
Other	306
Deferred income taxes	$ 27,275	$ 12,662	$ 20,883