Selected Balance Sheet Data

9 Months Ended

Sep. 30, 2016

Balance Sheet Related Disclosures [Abstract]

Selected Balance Sheet Data

Selected Balance Sheet Data

(Thousands of Dollars)	Sept. 30, 2016			Dec. 31, 2015
Accounts receivable, net (a)
Accounts receivable	$	52,270		$	61,506
Less allowance for bad debts	(4,459		)	(5,128		)
	$	47,811		$	56,378

(Thousands of Dollars)	Sept. 30, 2016		Dec. 31, 2015
Inventories
Materials and supplies	$	7,100	$	6,785
Fuel	4,887		6,528
Natural gas	8,282		8,246
	$	20,269	$	21,559

(Thousands of Dollars)	Sept. 30, 2016			Dec. 31, 2015
Property, plant and equipment, net
Electric plant	$	2,471,420		$	2,411,562
Natural gas plant	285,829			275,376
Common and other property	134,988			132,329
Construction work in progress	117,543			65,755
Total property, plant and equipment	3,009,780			2,885,022
Less accumulated depreciation	(1,108,084		)	(1,056,943		)
	$	1,901,696		$	1,828,079

^(a)  Accounts receivable, net includes an immaterial amount due from affiliates as of Sept. 30, 2016 and Dec. 31, 2015, respectively.