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Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2012
Asset Retirement Obligation Disclosure [Abstract]  
Asset Retirement Obligations
Asset Retirement Obligations
The ARO is recorded based on the determination of underlying assumptions, such as discount rates, estimates of the future costs for decommissioning, and the timing of the removal activities to be performed. Any changes in these assumptions underlying the required calculations may require revisions to the estimated ARO when identified. A reconciliation of ARO is as follows:
 
 
PNMR
 
PNM
 
TNMP
 
(In thousands)
Liability at December 31, 2009
$
70,963

 
$
70,099

 
$
771

Liabilities incurred
532

 
531

 
—

Liabilities settled
(603
)
 
(413
)
 
(190
)
Accretion expense
6,019

 
5,945

 
67

Revisions to estimated cash flows (1)
(274
)
 
(274
)
 
—

Liability at December 31, 2010
76,637

 
75,888

 
648

Liabilities incurred
60

 
60

 
—

Liabilities settled
(4
)
 
—

 
(4
)
Accretion expense
6,114

 
6,051

 
55

Revisions to estimated cash flows (1)
(3,574
)
 
(3,574
)
 
—

Liability at December 31, 2011
79,233

 
78,425

 
699

Liabilities incurred
—

 
—

 
—

Liabilities settled
(25
)
 
—

 
(25
)
Accretion expense
6,685

 
6,617

 
58

Liability at December 31, 2012
$
85,893

 
$
85,042

 
$
732

 

(1) 
Based on studies to estimate amount and timing of future ARO expenditures. PNM has an ARO for PVNGS that includes the obligations for nuclear decommissioning of that facility. In 2011, a new decommissioning study for PVNGS reflects updated cash flow estimates and the 20-year license extension, which extends the commencement of decommissioning to 2045. The new study resulted in a $4.2 million decrease to the ARO.