Selected Balance Sheet Data

9 Months Ended

Sep. 30, 2015

Balance Sheet Related Disclosures [Abstract]

Selected Balance Sheet Data

Selected Balance Sheet Data

(Thousands of Dollars)	Sept. 30, 2015			Dec. 31, 2014
Accounts receivable, net (a)
Accounts receivable	$	55,204		$	66,217
Less allowance for bad debts	(4,834		)	(5,821		)
	$	50,370		$	60,396

(Thousands of Dollars)	Sept. 30, 2015		Dec. 31, 2014
Inventories
Materials and supplies	$	6,865	$	6,494
Fuel	6,376		6,654
Natural gas	8,597		11,537
	$	21,838	$	24,685

(Thousands of Dollars)	Sept. 30, 2015			Dec. 31, 2014
Property, plant and equipment, net
Electric plant	$	2,332,155		$	2,061,669
Natural gas plant	264,390			255,465
Common and other property	124,584			125,938
Construction work in progress	112,108			231,413
Total property, plant and equipment	2,833,237			2,674,485
Less accumulated depreciation	(1,043,903		)	(1,000,204		)
	$	1,789,334		$	1,674,281

^(a)  Accounts receivable, net includes an immaterial amount due from affiliates as of Sept. 30, 2015 and Dec. 31, 2014, respectively.