Earnings and Dividends Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Earnings Attributable to PNMR									$ 172,775	$ 77,362	$ 85,642
Average Number of Common Shares:
Outstanding during year (in shares)									79,941	79,654	79,654
Vested awards of restricted stock (in shares)									216	277	236
Average Shares – Basic (in shares)									80,157	79,931	79,890
Dilutive Effect of Common Stock Equivalents:
PNMR 2020 Forward Equity Sale Agreements (in shares)									106	0	0
Stock options and restricted stock (in shares)									40	59	122
Average Shares – Diluted (in shares)									80,303	79,990	80,012
Net Earnings Attributable to PNMR Per Share of Common Stock:
Basic (in dollars per share)	$ 0.11	$ 1.52	$ 0.72	$ (0.19)	$ 0.40	$ 1.29	$ (0.95)	$ 0.23	$ 2.16	$ 0.97	$ 1.07
Diluted (in dollars per share)	$ 0.10	$ 1.52	$ 0.72	$ (0.19)	$ 0.40	$ 1.28	$ (0.95)	$ 0.23	2.15	0.97	1.07
Dividends Declared per Common Share (in dollars per share)									$ 1.2500	$ 1.1775	$ 1.0850