Selected Balance Sheet Data (Tables)

3 Months Ended

Mar. 31, 2013

Selected Balance Sheet Data [Abstract]

Accounts Receivable, Net

(Thousands of Dollars)	March 31, 2013			Dec. 31, 2012
Accounts receivable, net (a)
Accounts receivable	$	65,605		$	55,039
Less allowance for bad debts		(4,445	)		(4,333	)
	$	61,160		$	50,706

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

Inventories

(Thousands of Dollars)	March 31, 2013		Dec. 31, 2012
Inventories
Materials and supplies	$	6,191	$	6,172
Fuel		7,772		6,664
Natural gas		1,089		6,849
	$	15,052	$	19,685

Property, Plant and Equipment, Net

(Thousands of Dollars)	March 31, 2013			Dec. 31, 2012
Property, plant and equipment, net
Electric plant	$	1,817,310		$	1,795,239
Natural gas plant		226,657			224,625
Common and other property		110,715			111,319
Construction work in progress		71,527			62,629
Total property, plant and equipment		2,226,209			2,193,812
Less accumulated depreciation		(908,604	)		(895,576	)
	$	1,317,605		$	1,298,236