Pension and Other Postretirement Benefits - Other Postretirement Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
401(k) plan
Defined Contribution Plan [Abstract]
401(k) plan	$ 16,097	$ 16,677	$ 16,452
401(k) plan | Public Service Company of New Mexico
Defined Contribution Plan [Abstract]
401(k) plan	11,587	12,052	12,120
401(k) plan | Texas-New Mexico Power Company
Defined Contribution Plan [Abstract]
401(k) plan	4,511	4,625	4,332
Non-qualified plan
Defined Contribution Plan [Abstract]
Non-qualified plan	4,551	865	3,702
Non-qualified plan | Public Service Company of New Mexico
Defined Contribution Plan [Abstract]
Non-qualified plan	3,384	621	2,834
Non-qualified plan | Texas-New Mexico Power Company
Defined Contribution Plan [Abstract]
Non-qualified plan	$ 1,167	$ 244	$ 868