Regulatory Assets and Liabilities Regulatory Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	$ 101,050		$ 101,590
Total regulatory liabilities	26,416		22,179
Regulatory tax assets or liabilities
Regulatory Assets and Liabilities [Line Items]
Total regulatory liabilities	17,752	[1],[2]	16,666	[1],[2]
Accumulated Deferred Investment Tax Credit
Regulatory Assets and Liabilities [Line Items]
Total regulatory liabilities	4,656	[1],[3]	4,587	[1],[3]
New Mexico energy efficiency
Regulatory Assets and Liabilities [Line Items]
Total regulatory liabilities	3,646	[4]	926	[4]
Texas energy efficiency
Regulatory Assets and Liabilities [Line Items]
Total regulatory liabilities	362	[4]	0	[4]
Regulatory tax assets or liabilities
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	61,772	[1],[2]	57,551	[1],[2]
Loss on reacquired debt
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	18,338	[5]	19,191	[5]
Final coal reclamation
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	4,290	[6]	5,473	[6]
Nuclear fuel postload daily financing charge
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	4,141	[7]	3,833	[7]
Unrecovered issuance costs due to reissuance of PCBs
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	893	[5]	926	[5]
Texas energy efficiency
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	0	[4]	536	[4]
Texas 2012 rate case costs
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	581	[6]	2,335	[6]
Texas military base discount and recovery factor
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	759	[8]	2,116	[8]
New Mexico procurement plan costs
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	139	[9]	139	[9]
New Mexico renewable energy credits
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	4,833	[9]	4,033	[9]
New Mexico 2010 FPPCAC audit
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	433	[9]	433	[9]
New Mexico Palo Verde deferred depreciation
Regulatory Assets and Liabilities [Line Items]
Total regulatory assets	$ 4,871	[1]	$ 5,024	[1]

[1] The amortization period for this asset is based upon the life of the associated assets or liabilities.

[2] No specific return on investment is required since related assets and liabilities offset.

[3] This item is excluded from rate base.

[4] This item is recovered or credited through a recovery factor that is set annually.

[5] This item is recovered as a component of the weighted cost of debt and amortized over the life of the related debt issuance.

[6] This item is included in rate base which earns a return on investment.

[7] This item is recovered through fuel recovery mechanisms.

[8] This item represents the net asset related to the military discount which is recovered from non-military customers through a recovery factor.

[9] Amortization period is anticipated to be established in next general rate case.