Selected Balance Sheet Data

12 Months Ended

Dec. 31, 2015

Balance Sheet Related Disclosures [Abstract]

Selected Balance Sheet Data

Selected Balance Sheet Data

(Thousands of Dollars)	Dec. 31, 2015			Dec. 31, 2014
Accounts receivable, net
Accounts receivable	$	77,054		$	77,465
Less allowance for bad debts	(5,888		)	(5,839		)
	$	71,166		$	71,626

(Thousands of Dollars)	Dec. 31, 2015		Dec. 31, 2014
Inventories
Materials and supplies	$	24,888	$	24,738
Fuel	12,658		18,493
	$	37,546	$	43,231

(Thousands of Dollars)	Dec. 31, 2015			Dec. 31, 2014
Property, plant and equipment, net
Electric plant	$	5,933,764		$	5,376,606
Construction work in progress	236,697			238,519
Total property, plant and equipment	6,170,461			5,615,125
Less accumulated depreciation	(1,821,638		)	(1,871,984		)
	$	4,348,823		$	3,743,141