Equity Method Investment - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Results of Operations
Operating revenues	$ 554,551	$ 472,465	$ 1,345,798	$ 1,163,736
Financial Position
Construction work in progress	350,090		350,090		$ 218,719
Assets	8,256,070	7,742,112	8,256,070	7,742,112	7,939,854
Total stockholders' equity	2,144,950		2,144,950		2,049,465
NMRD
Results of Operations
Operating revenues	3,543	3,462	10,179	7,769
Operating expenses	2,422	2,100	7,360	5,152
Net Earnings Attributable to PNMR	1,121	$ 1,362	2,819	$ 2,617
Financial Position
Current assets	9,164		9,164		8,046
Construction work in progress	168,053		168,053		172,585
Non-current assets	2,448		2,448		1,900
Assets	179,665		179,665		182,531
Current liabilities	1,166		1,166		841
Non-current liabilities	370		370		380
Total stockholders' equity	$ 178,129		$ 178,129		$ 181,310