Lease Commitments - Narrative (Details) $ in Thousands	1 Months Ended	6 Months Ended
	Apr. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	May 16, 2019 MW	Dec. 31, 2018 USD ($)	Sep. 30, 2016 MW	Sep. 28, 2016 MW	Aug. 31, 2016 MW	Jan. 31, 2016 MW	Jan. 16, 2016 lease	Jan. 15, 2015 lease
Operating Leased Assets [Line Items]
Operating leases, capitalized financing costs, investing activities		$ 2,000
Finance leases, capitalized financing costs, investing activities		200
Lessee, operating lease, unguaranteed residual value		21,600
Operating lease, unguaranteed residual value				$ 18,500
PNM
Operating Leased Assets [Line Items]
Operating leases, capitalized financing costs, investing activities		700
Finance leases, capitalized financing costs, investing activities		100
Lessee, operating lease, unguaranteed residual value		8,600
Operating lease, unguaranteed residual value				$ 7,500
PNM | Palo Verde Nuclear Generating Station, Unit 1 and 4 Leases
Operating Leased Assets [Line Items]
Number of leases, expiring | lease										4
Number of leases under which lease term was extended | lease										4
Annual lease payments during renewal period		16,500
PNM | Navajo Nation
Operating Leased Assets [Line Items]
Annual lease payments		6,000
Right-of-way lease payments	$ 6,900
PNM | Palo Verde Nuclear Generating Station, Unit 2 Leases
Operating Leased Assets [Line Items]
Number of leases, expiring | lease									4
Number of leases under which lease term was extended | lease									1
Annual lease payments during renewal period		1,600
Number of megawatts purchased (in megawatts) | MW					64.1	64.1	64.1	64.1
Number of megawatts nuclear generation (in megawatts) | MW			114.6		114.6	114.6	114.6
PNM | Palo Verde Nuclear Generating Station
Operating Leased Assets [Line Items]
Restriction on conveying, transferring, leasing and dividends				5.00%
Loss contingency, lease arrangements (up to)		161,200
TNMP
Operating Leased Assets [Line Items]
Operating leases, capitalized financing costs, investing activities		1,300
Finance leases, capitalized financing costs, investing activities		100
Lessee, operating lease, unguaranteed residual value		12,900
Operating lease, unguaranteed residual value				$ 11,000
Equipment
Operating Leased Assets [Line Items]
Operating lease, residual value of leased asset		1,600
Equipment | PNM
Operating Leased Assets [Line Items]
Operating lease, residual value of leased asset		500
Equipment | TNMP
Operating Leased Assets [Line Items]
Operating lease, residual value of leased asset		$ 1,100