Lease Commitments - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lease, Cost [Line Items]
Operating lease cost:	$ 7,735	$ 8,620
Less: amounts capitalized	(925)	(1,009)
Total operating lease expense	6,810	7,611
Financing lease cost:
Amortization of right-of-use assets	553	203
Interest on lease liabilities	103	32
Less: amounts capitalized	(458)	(78)
Total financing lease expense	198	157
Variable lease expense	32	0
Short-term lease expense	86	94
Total lease expense for the period	7,126	7,862
PNM
Lease, Cost [Line Items]
Operating lease cost:	6,893	7,583
Less: amounts capitalized	(291)	(352)
Total operating lease expense	6,602	7,231
Financing lease cost:
Amortization of right-of-use assets	247	104
Interest on lease liabilities	45	16
Less: amounts capitalized	(175)	(38)
Total financing lease expense	117	82
Variable lease expense	32	0
Short-term lease expense	85	74
Total lease expense for the period	6,836	7,387
TNMP
Lease, Cost [Line Items]
Operating lease cost:	774	898
Less: amounts capitalized	(634)	(657)
Total operating lease expense	140	241
Financing lease cost:
Amortization of right-of-use assets	289	98
Interest on lease liabilities	56	17
Less: amounts capitalized	(283)	(40)
Total financing lease expense	62	75
Variable lease expense	0	0
Short-term lease expense	1	3
Total lease expense for the period	$ 203	$ 319