Income Tax (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

Dollars in thousands	2017			2016			2015
Income taxes at federal statutory rate	$	39,578		$	36,901		$	34,977
Increase (decrease):
State income tax, net of federal	5,066			4,844			4,683
Amortization of investment tax credits	(4		)	(41		)	(118		)
Differences required to be flowed-through by regulatory commissions	2,357			2,357			2,357
Gains on company and trust-owned life insurance	(872		)	(594		)	(766		)
Effect of TCJA	(3,376		)	—			—
Other, net	(1,741		)	(456		)	(1,227		)
Total provision for income taxes	$	41,008		$	43,011		$	39,906
Effective tax rate	36.3		%	40.8		%	39.9		%

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

In thousands	2017		2016		2015
Current
Federal	$	19,345	$	10,042	$	15,056
State	5,963		3,116		2,346
	25,308		13,158		17,402
Deferred
Federal	13,869		25,473		17,659
State	1,831		4,380		4,845
	15,700		29,853		22,504
Total provision for income taxes (loss benefits)	$	41,008	$	43,011	$	39,906

Schedule Of Regulated Utility And Non Utility Business Segments [Table Text Block]

In thousands	2017			2016			2015
Utility:
Current	$	21,453		$	10,300		$	15,890
Deferred	19,479			28,749			20,834
Deferred investment tax credits	(4		)	(41		)	(118		)
	40,928			39,008			36,606
Non-utility:
Current	3,855			2,859			1,512
Deferred	(3,775		)	1,144			1,788
	80			4,003			3,300
Total provision for income taxes	$	41,008		$	43,011		$	39,906

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

In thousands	2017		2016
Deferred tax liabilities:
Plant and property	$	296,114	$	428,642
Regulatory income tax assets	22,209		43,048
Regulatory liabilities	29,114		48,291
Non-regulated deferred tax liabilities	933		51,446
Total	$	348,370	$	571,427
Deferred tax assets:
Regulatory income tax liabilities	$	56,470	$	—
Non-regulated deferred tax assets	17,796		—
Pension and postretirement obligations	3,512		4,493
Alternative minimum tax credit carryforward	66		9,853
Total	$	77,844	$	14,346
Deferred income tax liabilities, net	$	270,526	$	557,081
Deferred investment tax credits	—		4
Deferred income taxes and investment tax credits	$	270,526	$	557,085