Selected Balance Sheet Data (Tables)

9 Months Ended

Sep. 30, 2012

Selected Balance Sheet Data [Abstract]

(Thousands of Dollars)	Sept. 30, 2012			Dec. 31, 2011
Accounts receivable, net
Accounts receivable	$	287,169		$	341,737
Less allowance for bad debts		(22,025	)		(24,698	)
	$	265,144		$	317,039

Inventories

(Thousands of Dollars)	Sept. 30, 2012		Dec. 31, 2011
Inventories
Materials and supplies	$	53,851	$	53,318
Fuel		96,647		94,874
Natural gas		91,946		105,805
	$	242,444	$	253,997

Property, Plant and Equipment, Net

(Thousands of Dollars)	Sept. 30, 2012			Dec. 31, 2011
Property, plant and equipment, net
Electric plant	$	9,741,933		$	9,469,434
Natural gas plant		2,535,274			2,456,275
Common and other property		748,553			763,513
Plant to be retired (a)		105,573			151,184
Construction work in progress		490,561			242,095
Total property, plant and equipment		13,621,894			13,082,501
Less accumulated depreciation		(3,776,988	)		(3,606,930	)
	$	9,844,906		$	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 retired, and in May 2012, Cherokee Unit 1 was retired. Amounts are presented net of accumulated depreciation.