Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Related Party Transaction [Line Items]
Ownership percentage	50.00%		50.00%
Services billings: | PNMR to PNM
Related Party Transaction [Line Items]
Amount of related party transaction	$ 22,471	$ 23,190	$ 46,150	$ 47,593
Services billings: | PNMR to TNMP
Related Party Transaction [Line Items]
Amount of related party transaction	8,058	7,806	16,423	15,943
Services billings: | PNM to TNMP
Related Party Transaction [Line Items]
Amount of related party transaction	90	102	177	187
Services billings: | TNMP to PNMR
Related Party Transaction [Line Items]
Amount of related party transaction	35	35	70	70
Services billings: | TNMP to PNM
Related Party Transaction [Line Items]
Amount of related party transaction	0	57	0	145
Services billings: | PNMR to NMRD
Related Party Transaction [Line Items]
Amount of related party transaction	51	0	130	0
Renewable energy purchases: | PNM from NMRD
Related Party Transaction [Line Items]
Amount of related party transaction	1,004	0	1,374	0
Interconnection billings: | PNM from NMRD
Related Party Transaction [Line Items]
Amount of related party transaction	2,052	0	2,052	0
Interconnection billings: | PNM to PNMR
Related Party Transaction [Line Items]
Amount of related party transaction	68,200	0	68,200	0
Interest billings: | PNMR to PNM
Related Party Transaction [Line Items]
Amount of related party transaction	747	9	809	11
Interest billings: | PNMR to TNMP
Related Party Transaction [Line Items]
Amount of related party transaction	13	30	22	60
Interest billings: | PNM to PNMR
Related Party Transaction [Line Items]
Amount of related party transaction	70	49	136	92
Income tax sharing payments: | PNMR to PNM
Related Party Transaction [Line Items]
Amount of related party transaction	0	0	0	0
Income tax sharing payments: | TNMP to PNMR
Related Party Transaction [Line Items]
Amount of related party transaction	$ 0	$ 0	$ 0	$ 0