Income Taxes - Interest Income (Expense) Related to Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Interest income related to income taxes	$ 0	$ 4,398	$ 0
Public Service Company of New Mexico
Income Taxes [Line Items]
Interest income related to income taxes	0	3,625	0
Texas-New Mexico Power Company
Income Taxes [Line Items]
Interest income related to income taxes	$ 0	345	$ 0
Interest income and interest expense applicable to federal income tax matters
Income Taxes [Line Items]
Net refunds received		6,500
Increase (decrease) of net interest receivable		(2,100)
Interest income		5,100
Interest expense		700
Professional fees		900
Net pre-tax impacts		3,500
Interest income and interest expense applicable to federal income tax matters | Public Service Company of New Mexico
Income Taxes [Line Items]
Net pre-tax impacts		2,600
Interest income and interest expense applicable to federal income tax matters | Texas-New Mexico Power Company
Income Taxes [Line Items]
Net pre-tax impacts		300
Interest income and interest expense applicable to federal income tax matters | Corporate and Other
Income Taxes [Line Items]
Net pre-tax impacts		$ 600