Selected Balance Sheet Data (Tables)

6 Months Ended

Jun. 30, 2012

Selected Balance Sheet Data [Abstract]

Accounts Receivable

(Thousands of Dollars)	June 30, 2012			Dec. 31, 2011
Accounts receivable, net
Accounts receivable	$	49,827		$	56,604
Less allowance for bad debts		(3,943	)		(4,766	)
	$	45,884		$	51,838

Inventories

(Thousands of Dollars)		June 30, 2012		Dec. 31, 2011
Inventories
Materials and supplies	$	6,072	$	5,838
Fuel		8,934		9,335
Natural gas		3,001		10,530
	$	18,007	$	25,703

Property, Plant and Equipment

(Thousands of Dollars)		June 30, 2012			Dec. 31, 2011
Property, plant and equipment, net
Electric plant	$	1,725,905		$	1,684,537
Natural gas plant		217,159			213,665
Common and other property		109,588			113,597
Construction work in progress		62,835			54,627
Total property, plant and equipment		2,115,487			2,066,426
Less accumulated depreciation		(872,049	)		(858,728	)
	$	1,243,438		$	1,207,698