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Selected Balance Sheet Data
 3 Months Ended
Mar. 31, 2012
Selected Balance Sheet Data [Abstract]  
Selected Balance Sheet Data
3.
Selected Balance Sheet Data

(Thousands of Dollars)
 
March 31, 2012
   
Dec. 31, 2011
 
Accounts receivable, net
         
Accounts receivable
 
$
306,973
   
$
341,737
 
Less allowance for bad debts
   
(24,288
)
   
(24,698
)
   
$
282,685
   
$
317,039
 
Inventories
               
Materials and supplies
 
$
54,262
   
$
53,318
 
Fuel
   
79,382
     
94,874
 
Natural gas
   
63,517
     
105,805
 
   
$
197,161
   
$
253,997
 
Property, plant and equipment, net
               
Electric plant
 
$
9,497,757
   
$
9,469,434
 
Natural gas plant
   
2,476,727
     
2,456,275
 
Common and other property
   
752,389
     
763,513
 
Plant to be retired (a)
   
115,401
     
151,184
 
Construction work in progress
   
317,958
     
242,095
 
Total property, plant and equipment
   
13,160,232
     
13,082,501
 
Less accumulated depreciation
   
(3,621,444
)
   
(3,606,930
)
   
$
9,538,788
   
$
9,475,571
 

(a)
In 2010, in response to the Clean Air Clean Jobs Act (CACJA), the Colorado Public Utilities Commission (CPUC) approved the early retirement of Cherokee Units 1, 2 and 3, Arapahoe Unit 3 and Valmont Unit 5 between 2011 and 2017.  In 2011, Cherokee Unit 2 was taken out of service.  Amounts are presented net of accumulated depreciation.