Variable Interest Entities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) MW	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jan. 31, 2016 USD ($)
Results of Operations
Operating revenues	$ 333,622	$ 349,645
Operating expenses	285,884	312,922
Earnings attributable to non-controlling interest	3,729	2,830
Financial Position
Current assets	287,962		$ 294,010
Assets	7,375,119	7,250,758	7,298,774
Current liabilities	1,114,920		967,481
Owners’ equity – non-controlling interest	60,347		63,052
PNM
Results of Operations
Operating revenues	248,133	269,318
Operating expenses	214,528	245,025
Earnings attributable to non-controlling interest	3,729	2,830
Financial Position
Current assets	245,755		259,195
Assets	5,260,528		5,242,991
Current liabilities	396,324		593,236
Owners’ equity – non-controlling interest	60,347		63,052
PNM | Valencia
Variable Interest Entity [Line Items]
Payment for fixed costs	5,000	4,900
Payment for variable costs	$ 400	100
Long-term contract option to purchase, ownership percentage (up to)	50.00%
Long-term contract option to purchase, purchase price - percentage of adjusted NBV	50.00%
Long-term contract option to purchase, purchase price - percentage of FMV	50.00%
PNM | Valencia
Results of Operations
Operating revenues	$ 5,353	4,952
Operating expenses	1,624	2,122
Earnings attributable to non-controlling interest	3,729	$ 2,830
Financial Position
Current assets	3,297		5,094
Net property, plant, and equipment	57,871		58,581
Assets	61,168		63,675
Current liabilities	821		623
Owners’ equity – non-controlling interest	$ 60,347		$ 63,052
PNM | Purchased through May 2028 | Valencia
Variable Interest Entity [Line Items]
Number of megawatts purchased (in megawatts) | MW	158
NM Capital | San Juan Generating Station | Coal supply
Variable Interest Entity [Line Items]
Cash used to support bank letter or credit arrangement	$ 30,300			$ 30,300