Fair Value of Derivative and Other Financial Instruments - Investment in NDT and Gross Realized Losses (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Equity securities:
Net gains from equity securities sold	$ 8,738	$ 5,861	$ 5,698
Net gains (losses) from equity securities still held	(442)	17,707	18,319
Total net gains on equity securities	8,296	23,568	24,017
Available-for-sale debt securities:
Net gains (losses) on debt securities	8,554	(1,969)	5,572
Net gains on investment securities	16,850	21,599	29,589
Public Service Company of New Mexico
Available-for-sale debt securities:
Proceeds from sales	459,867	590,998	494,528
Gross realized gains	39,408	35,904	25,760
Gross realized (losses)	$ (22,815)	$ (28,817)	$ (17,453)

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