Lease Commitments - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lease, Cost [Line Items]
Operating lease cost:	$ 7,545	$ 7,725	$ 22,938	$ 24,051
Amounts capitalized	(825)	(949)	(2,599)	(2,964)
Total operating lease expense	6,720	6,776	20,339	21,087
Financing lease cost:
Amortization of right-of-use assets	893	274	2,187	556
Interest on lease liabilities	134	54	358	117
Amounts capitalized	(733)	(195)	(1,787)	(391)
Total financing lease expense	294	133	758	282
Variable lease expense	63	32	158	64
Short-term lease expense	22	68	183	263
Total lease expense for the period	7,099	7,009	21,438	21,696
PNM
Lease, Cost [Line Items]
Operating lease cost:	6,798	6,873	20,538	21,260
Amounts capitalized	(248)	(319)	(786)	(1,015)
Total operating lease expense	6,550	6,554	19,752	20,245
Financing lease cost:
Amortization of right-of-use assets	435	143	1,022	286
Interest on lease liabilities	58	26	156	56
Amounts capitalized	(281)	(81)	(682)	(158)
Total financing lease expense	212	88	496	184
Variable lease expense	63	32	158	64
Short-term lease expense	16	63	176	212
Total lease expense for the period	6,841	6,737	20,582	20,705
TNMP
Lease, Cost [Line Items]
Operating lease cost:	685	726	2,205	2,439
Amounts capitalized	(577)	(630)	(1,812)	(1,949)
Total operating lease expense	108	96	393	490
Financing lease cost:
Amortization of right-of-use assets	439	125	1,110	264
Interest on lease liabilities	74	27	198	61
Amounts capitalized	(452)	(114)	(1,105)	(233)
Total financing lease expense	61	38	203	92
Variable lease expense	0	0	0	0
Short-term lease expense	4	5	5	10
Total lease expense for the period	$ 173	$ 139	$ 601	$ 592