Variable Interest Entities (Details) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended					1 Months Ended	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended						3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Public Service Company of New Mexico [Member]	Jun. 30, 2013 Public Service Company of New Mexico [Member]	Jun. 30, 2014 Public Service Company of New Mexico [Member]	Jun. 30, 2013 Public Service Company of New Mexico [Member]	Dec. 31, 2013 Public Service Company of New Mexico [Member]	Jun. 30, 2014 Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2014 Palo Verde Nuclear Generating Station [Member] Property Lease Guarantee [Member] Maximum [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2012 Delta [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2014 Delta [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2013 Delta [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2014 Delta [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2013 Delta [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2013 Delta [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2014 Valencia [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2013 Valencia [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2014 Valencia [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2013 Valencia [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2013 Valencia [Member] Public Service Company of New Mexico [Member]	Oct. 08, 2013 Valencia [Member] Public Service Company of New Mexico [Member]	May 30, 2008 Valencia [Member] Purchased Through May 30, 2028 [Member] Public Service Company of New Mexico [Member] MW	Jun. 30, 2014 Variable Interest Entity, Not Primary Beneficiary [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2014 Delta [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2013 Delta [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2014 Delta [Member] Public Service Company of New Mexico [Member]	Jun. 30, 2013 Delta [Member] Public Service Company of New Mexico [Member]
Variable Interest Entity [Line Items]
Number of mega watts purchased (in megawatts)																									158
Long Term Contract For Purchase of Electric Power Fixed Costs																			$ 4,800,000	$ 4,700,000	$ 9,600,000	$ 9,400,000					$ 1,600,000	$ 1,600,000	$ 3,200,000	$ 3,200,000
Long Term Contract For Purchase of Electric Power Variable Charges																			500,000	200,000	700,000	300,000					300,000	400,000	500,000	600,000
Variable Interest Entity, Statement Of Operation [Abstract]
Operating revenues																			5,307,000	4,922,000	10,238,000	9,697,000
Operating expenses																			(1,399,000)	(1,349,000)	(2,799,000)	(2,920,000)
Earnings attributable to non-controlling interest	3,908,000	3,573,000	7,439,000	6,777,000		3,908,000	3,573,000	7,439,000	6,777,000										3,908,000	3,573,000	7,439,000	6,777,000
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets	446,825,000		446,825,000		401,539,000	393,099,000		393,099,000		348,502,000									3,232,000		3,232,000		2,658,000
Net property, plant, and equipment																			73,729,000		73,729,000		75,137,000
Total assets	5,604,192,000	5,403,906,000	5,604,192,000	5,403,906,000	5,500,210,000	4,290,529,000		4,290,529,000		4,227,616,000									76,961,000		76,961,000		77,795,000
Current liabilities	486,869,000		486,869,000		492,671,000	226,303,000		226,303,000		357,266,000									682,000		682,000		766,000
Owners’ equity – non-controlling interest	76,279,000		76,279,000		77,029,000	76,279,000		76,279,000		77,029,000									76,279,000		76,279,000		77,029,000
Long term contract option to purchase, ownership percentage																			50.00%
Long term contract option to purchase, estimated purchase price																								85,000,000
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, approximate approval period																			15 months
Operating Leases, Renewal Options After Original Lease Term (in years)			6 years					2 years
Operating Leases, Extended Lease Term Option (in years)								6 years
Operating Leases, Future Minimum Payments Due											36,500,000
Operating leases, future minimum payments due, renewal term																										145,200,000
Loss Contingency, Range of Possible Loss, Portion Not Accrued												144,700,000.0
Operating Leases, Future Minimum Payments Due, Next Six Months											26,000,000
Period of Long Term Contract For Purchase of Electric Power Fixed Costs																											20 years
Long Term Contract for Purchase of Electric Power Aggregate Amount of Contract Remaining																											36,200,000		36,200,000
Payments to Acquire Businesses, Gross													22,800,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt														14,600,000		14,600,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets														22,400,000		22,400,000		23,700,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment														19,000,000		19,000,000		20,300,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities														16,500,000		16,500,000		18,200,000
Revenues														2,500,000	2,200,000	4,300,000	4,000,000
Net earnings	$ 29,141,000	$ 27,678,000	$ 41,609,000	$ 38,304,000		$ 20,346,000	$ 26,124,000	$ 28,021,000	$ 37,693,000					$ 300,000	$ 100,000	$ 600,000	$ 300,000