Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Deferred Tax Assets and Liabilities

The provisional tax effects of temporary differences that give rise to significant portions of the deferred tax assets and liabilities at December 31, 2017 and 2016 are presented below (in thousands):



	December 31,
	2017			2016
Deferred tax assets:
Benefit of tax loss carryforwards	$	24,035		$	60,749
Alternative minimum tax credit carryforward	16,620			16,620
Pensions and benefits	32,606			57,756
Asset retirement obligation	19,530			26,929
Regulatory liabilities related to income taxes	63,794			—
Deferred fuel	1,405			—
Total gross deferred tax assets	157,990			162,054
Deferred tax liabilities:
Plant, principally due to depreciation and basis differences	(426,077		)	(668,303		)
Decommissioning	(34,520		)	(43,463		)
Deferred fuel	—			(3,962		)
Other	(2,416		)	(1,392		)
Total gross deferred tax liabilities	(463,013		)	(717,120		)
Net accumulated deferred income taxes	$	(305,023	)	$	(555,066	)

Schedule of Components of Income Tax Expense (Benefit)

The Company recognized income tax expense for 2017, 2016 and 2015 as follows (in thousands):



	Years Ended December 31,
	2017			2016			2015
Income tax expense:
Federal:
Current	$	2,507		$	2,642		$	2,319
Deferred	46,089			47,909			32,819
Total federal income tax	48,596			50,551			35,138
State:
Current	(897		)	766			1,730
Deferred	1,816			3,285			(1,650		)
Total state income tax	919			4,051			80
Generation (amortization) of accumulated investment tax credits	1,489			(684		)	(323		)
Total income tax expense	$	51,004		$	53,918		$	34,895

Schedule of Effective Income Tax Rate Reconciliation

Income tax provisions differ from amounts computed by applying the statutory federal income tax rate of 35% to book income before federal income tax as follows (in thousands):



	Years Ended December 31,
	2017			2016			2015
Federal income tax expense computed on income at statutory rate	$	52,243		$	52,740		$	40,885
Difference due to:
State taxes, net of federal benefit	597			2,633			52
AEFUDC	450			(475		)	(2,345		)
Permanent tax differences	(2,562		)	(2,369		)	(2,898		)
Other	276			1,389			(799		)
Total income tax expense	$	51,004		$	53,918		$	34,895
Effective income tax rate	34.2		%	35.8		%	29.9		%

Summary of Income Tax Contingencies

A reconciliation of the December 31, 2017, 2016 and 2015 amounts of unrecognized tax benefits are as follows (in thousands):



	2017			2016			2015
Balance at January 1	$	5,300		$	6,000		$	5,200
Additions for tax positions related to the current year	200			400			500
Reductions for tax positions related to the current year	—			—			—
Additions for tax positions of prior years	400			100			300
Reductions for tax positions of prior years	(1,700		)	(1,200		)	—
Balance at December 31	$	4,200		$	5,300		$	6,000