Lease Commitments - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lease, Cost [Line Items]
Operating lease cost:	$ 7,692	$ 16,312
Less: amounts capitalized	(1,006)	(2,015)
Total operating lease expense	6,686	14,297
Financing lease cost:
Amortization of right-of-use assets	158	282
Interest on lease liabilities	31	64
Less: amounts capitalized	(79)	(157)
Total financing lease expense	110	189
Variable lease expense	32	32
Short-term lease expense	101	195
Total lease expense for the period	6,929	14,713
PNM
Lease, Cost [Line Items]
Operating lease cost:	6,803	14,386
Less: amounts capitalized	(344)	(696)
Total operating lease expense	6,459	13,690
Financing lease cost:
Amortization of right-of-use assets	77	143
Interest on lease liabilities	14	30
Less: amounts capitalized	(41)	(82)
Total financing lease expense	50	91
Variable lease expense	32	32
Short-term lease expense	75	149
Total lease expense for the period	6,616	13,962
TNMP
Lease, Cost [Line Items]
Operating lease cost:	815	1,713
Less: amounts capitalized	(662)	(1,319)
Total operating lease expense	153	394
Financing lease cost:
Amortization of right-of-use assets	81	139
Interest on lease liabilities	17	34
Less: amounts capitalized	(38)	(75)
Total financing lease expense	60	98
Variable lease expense	0	0
Short-term lease expense	2	5
Total lease expense for the period	$ 215	$ 497