Lease Commitments - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lease, Cost [Line Items]
Operating lease cost:	$ 7,658	$ 7,692	$ 15,393	$ 16,312
Amounts capitalized	(849)	(1,006)	(1,774)	(2,015)
Total operating lease expense	6,809	6,686	13,619	14,297
Financing lease cost:
Amortization of right-of-use assets	741	158	1,294	282
Interest on lease liabilities	121	31	224	64
Amounts capitalized	(594)	(79)	(1,053)	(157)
Total financing lease expense	268	110	465	189
Variable lease expense	63	32	95	32
Short-term lease expense	75	101	161	195
Total lease expense for the period	7,215	6,929	14,340	14,713
PNM
Lease, Cost [Line Items]
Operating lease cost:	6,847	6,803	13,740	14,386
Amounts capitalized	(247)	(344)	(538)	(696)
Total operating lease expense	6,600	6,459	13,202	13,690
Financing lease cost:
Amortization of right-of-use assets	341	77	588	143
Interest on lease liabilities	52	14	97	30
Amounts capitalized	(226)	(41)	(401)	(82)
Total financing lease expense	167	50	284	91
Variable lease expense	63	32	95	32
Short-term lease expense	75	75	160	149
Total lease expense for the period	6,905	6,616	13,741	13,962
TNMP
Lease, Cost [Line Items]
Operating lease cost:	746	815	1,521	1,713
Amounts capitalized	(602)	(662)	(1,237)	(1,319)
Total operating lease expense	144	153	284	394
Financing lease cost:
Amortization of right-of-use assets	382	81	672	139
Interest on lease liabilities	68	17	124	34
Amounts capitalized	(369)	(38)	(653)	(75)
Total financing lease expense	81	60	143	98
Variable lease expense	0	0	0	0
Short-term lease expense	1	2	1	5
Total lease expense for the period	$ 226	$ 215	$ 428	$ 497