Electric Operating Revenues - Changes in contract liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Change In Contract With Customer Liability [Roll Forward]
Beginning balance	$ 349
Consideration received in advance of service to be provided	5,370
Deferred revenue earned	(1,720)
Ending balance	3,999
PNM
Change In Contract With Customer Liability [Roll Forward]
Beginning balance	349
Consideration received in advance of service to be provided	3,981
Deferred revenue earned	(1,349)
Ending balance	2,981
TNMP
Change In Contract With Customer Liability [Roll Forward]
Beginning balance	0
Consideration received in advance of service to be provided	1,389
Deferred revenue earned	(371)
Ending balance	$ 1,018