Variable Interest Entities (Details) $ in Thousands	3 Months Ended	7 Months Ended	12 Months Ended
	Sep. 30, 2015	Jul. 16, 2014 USD ($)	Dec. 31, 2015 USD ($) InstitutionalInvestors MW	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jul. 17, 2014 USD ($)	Oct. 08, 2013 USD ($)	May. 30, 2008 USD ($)
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets			$ 385,570	$ 406,434
Total assets			6,009,328	5,790,237	$ 5,426,858
Current liabilities			641,120	704,087
Owners’ equity – non-controlling interest			71,407	73,546
Net Income (Loss) Attributable to Noncontrolling Interest			$ 14,910	14,127	14,521
Public Service Company of New Mexico [Member]
Variable Interest Entity [Line Items]
Number of different institutional investors of trust lessors | InstitutionalInvestors			5
Accrued lease payments			$ 28,496
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets			357,757	368,988
Total assets			4,599,344	4,453,114
Current liabilities			316,921	415,501
Owners’ equity – non-controlling interest			71,407	73,546
Net Income (Loss) Attributable to Noncontrolling Interest			$ 14,910	14,127	14,521
Public Service Company of New Mexico [Member] | Delta [Member]
Variable Interest Entity [Line Items]
Long term contract for purchase of electric power fixed costs		$ 3,500			6,400
Long term contract for purchase of electric power variable charges		600			1,800
Payments to acquire businesses, net		$ 22,800
Project financing debt, amount at closing						$ 14,600
Recorded plant in service						58,100
Accumulated depreciation						23,500
Current assets						3,600
Deferred charges						3,400
Current liabilities						300
Non-current regulatory liabilities						$ 3,400
Valencia [Member] | Public Service Company of New Mexico [Member]
Variable Interest Entity [Line Items]
Number of mega watts purchased (in megawatts) | MW			158
Power plant total construction costs								$ 90,000
Long term contract for purchase of electric power fixed costs			$ 17,500	19,100	18,900
Long term contract for purchase of electric power variable charges			$ 1,500	1,200	1,200
Long term contract option to purchase, purchase price - percentage of adjusted NBV			50.00%
Long term contract option to purchase, purchase price - percentage of FMV	50.00%
Long term contract option to purchase, number of days to set FMV			60 days
Long term contract option to purchase, estimated purchase price							$ 85,000
Long term contract option to purchase, approximate approval period			15 months
Long term contract option to purchase, ownership percentage			50.00%
Number of years the operating licenses for plants were extended			20 years
Variable Interest Entity, Statement Of Operation [Abstract]
Operating revenues			$ 20,687	20,247	20,166
Operating expenses			(5,777)	(6,120)	(5,645)
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets			2,588	2,513
Net property, plant and equipment			69,784	72,321
Total assets			72,372	74,834
Current liabilities			965	1,288
Owners’ equity – non-controlling interest			71,407	73,546
Net Income (Loss) Attributable to Noncontrolling Interest			$ 14,910	14,127	$ 14,521
Valencia [Member] | Public Service Company of New Mexico [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Jointly owned utility plant, option to purchase proportionate ownership share			50.00%				50.00%
PVNGS [Member] | Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member]
Variable Interest Entity [Line Items]
Accrued lease payments			$ 18,400	$ 26,000
Delta [Member] | Public Service Company of New Mexico [Member]
Variable Interest Entity [Line Items]
Period of long term contract for purchase of electric power, fixed costs			20 years