Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Related Party Transaction [Line Items]
Ownership percentage	50.00%
Services billings: | PNMR to PNM
Related Party Transaction [Line Items]
Amount of related party transaction	$ 26,826	$ 23,679
Services billings: | PNMR to TNMP
Related Party Transaction [Line Items]
Amount of related party transaction	10,058	8,365
Services billings: | PNM to TNMP
Related Party Transaction [Line Items]
Amount of related party transaction	75	86
Services billings: | TNMP to PNMR
Related Party Transaction [Line Items]
Amount of related party transaction	35	35
Services billings: | PNMR to NMRD
Related Party Transaction [Line Items]
Amount of related party transaction	41	78
Renewable energy purchases: | PNM from NMRD
Related Party Transaction [Line Items]
Amount of related party transaction	625	370
Interconnection billings: | PNM from NMRD
Related Party Transaction [Line Items]
Amount of related party transaction	0	0
Interconnection billings: | PNM to PNMR
Related Party Transaction [Line Items]
Amount of related party transaction	0	0
Interest billings: | PNMR to PNM
Related Party Transaction [Line Items]
Amount of related party transaction	933	62
Interest billings: | PNMR to TNMP
Related Party Transaction [Line Items]
Amount of related party transaction	32	8
Interest billings: | PNM to PNMR
Related Party Transaction [Line Items]
Amount of related party transaction	72	66
Income tax sharing payments: | PNMR to PNM
Related Party Transaction [Line Items]
Amount of related party transaction	0	0
Income tax sharing payments: | TNMP to PNMR
Related Party Transaction [Line Items]
Amount of related party transaction	$ 0	$ 0