Selected Balance Sheet Data

3 Months Ended

Mar. 31, 2015

Balance Sheet Related Disclosures [Abstract]

Selected Balance Sheet Data

Selected Balance Sheet Data

(Thousands of Dollars)	March 31, 2015			Dec. 31, 2014
Accounts receivable, net (a)
Accounts receivable	$	71,265		$	66,217
Less allowance for bad debts	(5,373		)	(5,821		)
	$	65,892		$	60,396

(Thousands of Dollars)	March 31, 2015		Dec. 31, 2014
Inventories
Materials and supplies	$	6,661	$	6,494
Fuel	6,958		6,654
Natural gas	1,236		11,537
	$	14,855	$	24,685

(Thousands of Dollars)	March 31, 2015			Dec. 31, 2014
Property, plant and equipment, net
Electric plant	$	2,152,862		$	2,061,669
Natural gas plant	257,471			255,465
Common and other property	125,153			125,938
Construction work in progress	194,488			231,413
Total property, plant and equipment	2,729,974			2,674,485
Less accumulated depreciation	(1,014,007		)	(1,000,204		)
	$	1,715,967		$	1,674,281

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