Equity Method Investment - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Results of Operations
Operating revenues	$ 426,540	$ 357,649	$ 791,247	$ 691,271
Financial Position
Construction work in progress	293,050		293,050		$ 218,719
Assets	8,120,469	7,574,467	8,120,469	7,574,467	7,939,854
Total stockholders' equity	2,088,231		2,088,231		2,049,465
NMRD
Results of Operations
Operating revenues	3,885	2,641	6,635	4,308
Operating expenses	2,416	1,472	4,938	3,052
Net Earnings Attributable to PNMR	1,469	$ 1,169	1,697	$ 1,256
Financial Position
Current assets	7,781		7,781		8,046
Construction work in progress	169,132		169,132		172,585
Non-current assets	1,503		1,503		1,900
Assets	178,416		178,416		182,531
Current liabilities	1,022		1,022		841
Non-current liabilities	387		387		380
Total stockholders' equity	$ 177,007		$ 177,007		$ 181,310