Equity Method Investment - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Income Statement [Abstract]
Revenues	$ 357,649	$ 330,228	$ 691,271	$ 679,872
Balance Sheet Related Disclosures [Abstract]
Construction work in progress	309,513		309,513		$ 161,106
Assets	7,574,467	7,048,667	7,574,467	7,048,667	7,298,774
Total stockholders' equity	1,696,500		1,696,500		1,678,698
NMRD
Income Statement [Abstract]
Revenues	2,641	1,103	4,308	1,828
Operating Expenses	1,472	655	3,052	1,451
Net Earnings (Loss) Attributable to PNMR	1,169	$ 448	1,256	$ 377
Balance Sheet Related Disclosures [Abstract]
Cash	5,672		5,672		7,187
Construction work in progress	163,629		163,629		132,772
Assets, Noncurrent	1,214		1,214		0
Assets	170,515		170,515		139,959
Accounts Payable	2,073		2,073		9,640
Liabilities, Noncurrent	368		368		0
Total stockholders' equity	$ 168,074		$ 168,074		$ 130,319