Selected Balance Sheet Data (Tables)

9 Months Ended

Sep. 30, 2013

Balance Sheet Related Disclosures [Abstract]

Accounts Receivable, Net

(Thousands of Dollars)	Sept. 30, 2013			Dec. 31, 2012
Accounts receivable, net (a)
Accounts receivable	$	52,596		$	55,039
Less allowance for bad debts	(4,477		)	(4,333		)
	$	48,119		$	50,706

^(a) Accounts receivable, net includes $14 and $586 due from affiliates as of Sept. 30, 2013 and Dec. 31, 2012, respectively.

Inventories

(Thousands of Dollars)	Sept. 30, 2013		Dec. 31, 2012
Inventories
Materials and supplies	$	6,406	$	6,172
Fuel	5,771		6,664
Natural gas	10,822		6,849
	$	22,999	$	19,685

Property, Plant and Equipment, Net

(Thousands of Dollars)	Sept. 30, 2013			Dec. 31, 2012
Property, plant and equipment, net
Electric plant	$	1,869,563		$	1,795,239
Natural gas plant	231,778			224,625
Common and other property	112,514			111,319
Construction work in progress	101,436			62,629
Total property, plant and equipment	2,315,291			2,193,812
Less accumulated depreciation	(936,644		)	(895,576		)
	$	1,378,647		$	1,298,236