Equity Method Investment - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Income Statement [Abstract]
Revenues	$ 333,622	$ 349,645
Balance Sheet Related Disclosures [Abstract]
Construction work in progress	240,002		$ 161,106
Assets	7,375,119	7,250,758	7,298,774
Total stockholders' equity	1,627,222		1,678,698
NMRD
Income Statement [Abstract]
Revenues	1,667	725
Operating Expenses	1,580	796
Net Earnings (Loss) Attributable to PNMR	87	$ (71)
Balance Sheet Related Disclosures [Abstract]
Cash	12,848		7,187
Construction work in progress	137,763		132,772
Assets, Noncurrent	1,548		0
Assets	152,159		139,959
Accounts Payable	1,392		9,640
Liabilities, Noncurrent	362		0
Total stockholders' equity	$ 150,405		$ 130,319