Summary of the Business and Significant Accounting Policies - Inventories/Depreciation and Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Public Utilities, Inventory [Line Items]
Inventory	$ 73,027	$ 67,386
Coal [Member]
Public Utilities, Inventory [Line Items]
Inventory	19,940	18,356
Materials and supplies [Member]
Public Utilities, Inventory [Line Items]
Inventory	53,087	49,030
Public Service Company of New Mexico [Member]
Public Utilities, Inventory [Line Items]
Inventory	64,401	60,477
Public Service Company of New Mexico [Member] | Coal [Member]
Public Utilities, Inventory [Line Items]
Inventory	19,940	18,356
Public Service Company of New Mexico [Member] | Materials and supplies [Member]
Public Utilities, Inventory [Line Items]
Inventory	$ 44,461	$ 42,121
Public Service Company of New Mexico [Member] | Electric plant [Member]
Public Utilities, Inventory [Line Items]
Depreciation average rates used	2.33%	2.27%	2.26%
Public Service Company of New Mexico [Member] | Common, intangible, and general plant [Member]
Public Utilities, Inventory [Line Items]
Depreciation average rates used	5.40%	4.66%	4.64%
Texas-New Mexico Power Company [Member]
Public Utilities, Inventory [Line Items]
Depreciation average rates used	3.66%	3.65%	3.59%
Inventory	$ 8,626	$ 6,909
Texas-New Mexico Power Company [Member] | Coal [Member]
Public Utilities, Inventory [Line Items]
Inventory	0	0
Texas-New Mexico Power Company [Member] | Materials and supplies [Member]
Public Utilities, Inventory [Line Items]
Inventory	$ 8,626	$ 6,909