Stockholders' Equity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Payment of dividends	$ 133,900
Line of Credit
Class of Stock [Line Items]
Debt-to-capital ratio (not more than)	65.00%
Public Service Company of New Mexico
Class of Stock [Line Items]
Equity contribution from parent	$ 0	$ 28,142	$ 175,000
Payment of dividends	$ 246,100
Preferred stock, dividend rate	4.58%
Preferred stock, redemption percent	102.00%
Preferred stock outstanding (in shares)	115,293	115,293
Preferred stock, cumulative shares authorized (in shares)	10,000,000	10,000,000
Public Service Company of New Mexico | Maximum
Class of Stock [Line Items]
Requirement to obtain approval to transfer more than a percentage of PNM's assets	5.00%
Public Service Company of New Mexico | Affiliated Entity
Class of Stock [Line Items]
Cash dividends paid to parent company by consolidated subsidiaries	$ 60,700	$ 4,100	94,400
Texas-New Mexico Power Company
Class of Stock [Line Items]
Equity contribution from parent	$ 50,000	50,000	0
Preferred stock, cumulative shares authorized (in shares)	1,000,000
Texas-New Mexico Power Company | Line of Credit
Class of Stock [Line Items]
Debt-to-capital ratio (not more than)	65.00%
Texas-New Mexico Power Company | Affiliated Entity
Class of Stock [Line Items]
Cash dividends paid to parent company by consolidated subsidiaries	$ 44,400	$ 31,800	$ 33,200
PNMR and TNMP
Class of Stock [Line Items]
Preferred stock outstanding (in shares)	0