Income Taxes (Details) - USD ($)	3 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2016	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
New Mexico Corporate tax rate before change in 2013							7.60%
New Mexico Corporate tax rate, effective by 2018						5.90%
Increase (decrease) in regulatory liability		$ (7,100,000)	$ (2,000,000)
Impairment of state net operating loss carryforward			1,000,000	$ 0
Interest income and interest expense applicable to federal income tax matters [Member]
Income Tax Contingency [Line Items]
Net refunds from the IRS	$ 6,500,000
Increase (decrease) of interest receivable	(2,100,000)
Interest income	5,100,000
Interest expense	700,000
Consulting expense fees	900,000
Net settlement with taxing authority, pre-tax	3,500,000
Corporate and Other [Member]
Income Tax Contingency [Line Items]
Increase (decrease) in tax expense due to tax rate change		(100,000)	(200,000)
Impairment of state net operating loss carryforward			300,000
Corporate and Other [Member] | Interest income and interest expense applicable to federal income tax matters [Member]
Income Tax Contingency [Line Items]
Net settlement with taxing authority, pre-tax, segment allocation	600,000
Public Service Company of New Mexico [Member] | Interest income and interest expense applicable to federal income tax matters [Member]
Income Tax Contingency [Line Items]
Net settlement with taxing authority, pre-tax, segment allocation	2,600,000
Texas-New Mexico Power Company [Member] | Interest income and interest expense applicable to federal income tax matters [Member]
Income Tax Contingency [Line Items]
Net settlement with taxing authority, pre-tax, segment allocation	300,000
Public Service Company of New Mexico [Member]
Income Tax Contingency [Line Items]
Increase (decrease) in deferred tax assets as a result of tax rate changes		(700,000)	700,000
Increase (decrease) in tax expense due to tax rate change		$ 800,000	(500,000)
Impairment of state net operating loss carryforward			$ 700,000
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member]
Income Tax Contingency [Line Items]
Approved recovery of net operating loss carryforward	$ 2,100,000
Texas-New Mexico Power Company [Member]
Income Tax Contingency [Line Items]
Impairment of state net operating loss carryforward					$ 0