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Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Summary of Effective Income Tax Rates

The components of income from continuing operations before income taxes for each of the three years ended December 31, 2015 and income tax expense (benefit) attributable thereto were as follows:

	Years Ended December 31,
(Thousands of dollars)	2015				2014				2013
Income (loss) from continuing operations before income taxes	$	218,289			$	339,346			$	254,194
Income tax expense (benefit)
Federal - Current	$	58,039			119,338				92,828
Federal - Deferred	15,853				(382		)		(9,067		)
State - Current and deferred	6,806				(2,570		)		16,298
Total	$	80,698			$	116,386			$	100,059

Schedule of Reconciliation of Income Taxes to Statutory Rate

The following table reconciles income taxes based on the U.S. statutory tax rate to the Company’s income tax expense.

	Years Ended December 31,
(Thousands of dollars)	2015				2014				2013
Income tax expense based on the U.S. statutory tax rate	$	76,401			$	118,771			$	88,968
State income taxes, net of federal benefit	4,424				(1,671		)		10,594
Other, net	(127		)		(714		)		497
Total	$	80,698			$	116,386			$	100,059

Summary of Deferred Tax Assets and Deferred Tax Liabilities

An analysis of the Company’s deferred tax assets and deferred tax liabilities at December 31, 2015 and 2014 showing the tax effects of significant temporary differences follows:

	December 31,
(Thousands of dollars)	2015				2014
Deferred tax assets
Property costs and asset retirement obligations	$	2,666			$	2,157
Employee benefits	9,647				9,712
Other deferred tax assets	7,297				8,995
Total gross deferred tax assets	19,610				20,864
Less valuation allowance	—				—
Net deferred tax assets	19,610				20,864
Deferred tax liabilities
Accumulated depreciation and amortization	(157,322		)		(133,535		)
State deferred taxes	(17,042		)		(16,855		)
Other deferred tax liabilities	(8,211		)		(8,837		)
Total gross deferred tax liabilities	(182,575		)		(159,227		)
Net deferred tax liabilities	$	(162,965	)		$	(138,363	)

Reconciliation of Beginning and Ending Liability for Uncertain Tax Positions

No uncertain tax position liabilities were recognized for the year ending December 31, 2013.

	Year Ended December 31,
(Thousands of dollars)	2015			2014
Balance at January 1	$	6,101		$	—
Additions for tax positions related to prior year	222			10,086
Additions for tax positions related to current year	—			77
Settlements with taxing authorities	—			(1,563		)
Expiration of statutes of limitation	(873		)	(2,499		)
Balance at December 31	$	5,450		$	6,101

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Tabular disclosure of the components of income tax expense attributable to continuing operations for each year presented including, but not limited to: current tax expense (benefit), deferred tax expense (benefit), investment tax credits, government grants, the benefits of operating loss carryforwards, tax expense that results from allocating certain tax benefits either directly to contributed capital or to reduce goodwill or other noncurrent intangible assets of an acquired entity, adjustments of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity, and adjustments of the beginning-of-the-year balances of a valuation allowance because of a change in circumstances that causes a change in judgment about the realizability of the related deferred tax asset in future years.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
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Tabular disclosure of the components of net deferred tax asset or liability recognized in an entity's statement of financial position, including the following: the total of all deferred tax liabilities, the total of all deferred tax assets, the total valuation allowance recognized for deferred tax assets.

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-Topic 740
-SubTopic 10
-Section 50
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Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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Tabular disclosure of the change in unrecognized tax benefits.

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-Publisher FASB
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-Topic 740
-SubTopic 10
-Section 55
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