Selected Balance Sheet Data (Tables)

12 Months Ended

Dec. 31, 2012

Selected Balance Sheet Data [Abstract]

Accounts Receivable, Net

(Thousands of Dollars)	Dec. 31, 2012			Dec. 31, 2011
Accounts receivable, net (a)
Accounts receivable	$	55,039		$	56,604
Less allowance for bad debts		(4,333	)		(4,766	)
	$	50,706		$	51,838

(a) Accounts receivable, net includes $586 due from affiliates as of Dec. 31, 2012.

Inventories

(Thousands of Dollars)	Dec. 31, 2012		Dec. 31, 2011
Inventories
Materials and supplies	$	6,172	$	5,838
Fuel		6,664		9,335
Natural gas		6,849		10,530
	$	19,685	$	25,703

Property, Plant and Equipment, Net

(Thousands of Dollars)	Dec. 31, 2012			Dec. 31, 2011
Property, plant and equipment, net
Electric plant	$	1,795,239		$	1,684,537
Natural gas plant		224,625			213,665
Common and other property		111,319			113,597
Construction work in progress		62,629			54,627
Total property, plant and equipment		2,193,812			2,066,426
Less accumulated depreciation		(895,576	)		(858,728	)
	$	1,298,236		$	1,207,698