Segments and Related Information (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Results from Operations by Reportable Segment

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
2017
Operating revenues (a)	$	881,891	$	122,353	$	1,207	$	—		$	1,005,451
Intersegment revenues	497		287		—		(784		)	—
Total revenues	$	882,388	$	122,640	$	1,207	$	(784	)	$	1,005,451
Depreciation and amortization	$	88,946	$	22,070	$	200	$	—		$	111,216
Interest charges and financing costs	29,396		2,761		23		—			32,180
Income tax expense	38,866		4,040		1,266		—			44,172
Net income	70,876		7,832		708		—			79,416

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other			Reconciling Eliminations			Consolidated Total
2016
Operating revenues (a)	$	849,946	$	106,157	$	1,130		$	—		$	957,233
Intersegment revenues	397		487		—			(884		)	—
Total revenues	$	850,343	$	106,644	$	1,130		$	(884	)	$	957,233
Depreciation and amortization	$	81,299	$	16,794	$	201		$	—		$	98,294
Interest charges and financing costs	29,749		2,855		25			—			32,629
Income tax expense (benefit)	40,547		2,445		(90		)	—			42,902
Net income (loss)	65,002		4,503		(370		)	—			69,135

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
2015
Operating revenues (a)	$	834,998	$	120,147	$	1,396	$	—		$	956,541
Intersegment revenues	419		498		—		(917		)	—
Total revenues	$	835,417	$	120,645	$	1,396	$	(917	)	$	956,541
Depreciation and amortization	$	77,036	$	14,034	$	175	$	—		$	91,245
Interest charges and financing costs	26,494		2,637		90		—			29,221
Income tax expense	40,654		2,501		1,083		—			44,238
Net income	69,398		4,862		376		—			74,636

^(a)  Operating revenuesinclude $177 million, $170 million and $163 million of intercompany revenue for the years ended Dec. 31, 2017, 2016 and 2015 respectively. See Note 15 for further discussion of related party transactions by operating segment.