Lease Commitments - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Lease, Cost [Line Items]
Operating lease cost:	$ 7,192	$ 7,545	$ 22,006	$ 22,938
Amounts capitalized	(716)	(825)	(2,264)	(2,599)
Total operating lease expense	6,476	6,720	19,742	20,339
Financing lease cost:
Amortization of right-of-use assets	1,372	893	3,802	2,187
Interest on lease liabilities	145	134	426	358
Amounts capitalized	(1,161)	(733)	(3,202)	(1,787)
Total financing lease expense	356	294	1,026	758
Variable lease expense	106	63	274	158
Short-term lease expense	1,578	22	1,857	183
Total lease expense for the period	8,516	7,099	22,899	21,438
Cooling Towers
Financing lease cost:
Short-term lease expense	1,400		1,400
Increase reimbursements	900		900
PNM
Lease, Cost [Line Items]
Operating lease cost:	6,569	6,798	20,020	20,538
Amounts capitalized	(199)	(248)	(645)	(786)
Total operating lease expense	6,370	6,550	19,375	19,752
Financing lease cost:
Amortization of right-of-use assets	657	435	1,793	1,022
Interest on lease liabilities	66	58	193	156
Amounts capitalized	(452)	(281)	(1,235)	(682)
Total financing lease expense	271	212	751	496
Variable lease expense	106	63	274	158
Short-term lease expense	1,572	16	1,821	176
Total lease expense for the period	8,319	6,841	22,221	20,582
TNMP
Lease, Cost [Line Items]
Operating lease cost:	594	685	1,880	2,205
Amounts capitalized	(517)	(577)	(1,618)	(1,812)
Total operating lease expense	77	108	262	393
Financing lease cost:
Amortization of right-of-use assets	693	439	1,944	1,110
Interest on lease liabilities	78	74	230	198
Amounts capitalized	(709)	(452)	(1,967)	(1,105)
Total financing lease expense	62	61	207	203
Variable lease expense	0	0	0	0
Short-term lease expense	2	4	6	5
Total lease expense for the period	$ 141	$ 173	$ 475	$ 601