INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2016

Income tax [Line Items]

Reconciliation of Income Tax Provision

The following table sets forth our provision for income taxes for the periods indicated:

	Years Ended December 31,
	2016			2015		2014
	(Thousands of dollars)
Current income tax provision
Federal	$	(2,016	)	$	7,135	$	17,006
State	471			2,055		1,397
Total current income tax provision	(1,545		)	9,190		18,403
Deferred income tax provision
Federal	76,247			56,440		42,024
State	10,541			7,349		7,911
Total deferred income tax provision	86,788			63,789		49,935
Total provision for income taxes	$	85,243		$	72,979	$	68,338

Schedule of Effective Income Tax Rate Reconciliation

The following table is a reconciliation of our income tax provision for the periods indicated:

	Years Ended December 31,
	2016			2015			2014
	(Thousands of dollars)
Income before income taxes	$	225,338		$	192,009		$	178,128
Federal statutory income tax rate	35		%	35		%	35		%
Provision for federal income taxes	78,868			67,203			62,345
State income taxes, net of federal tax benefit	7,158			6,114			6,051
Other, net	(783		)	(338		)	(58		)
Total provision for income taxes	$	85,243		$	72,979		$	68,338

Schedule of Deferred Tax Assets and Liabilities

The following table sets forth the tax effects of temporary differences that gave rise to significant portions of the deferred tax assets and liabilities for the periods indicated:

	December 31,
	2016		2015
	(Thousands of dollars)
Deferred tax assets
Employee benefits and other accrued liabilities	$	123,333	$	110,148
Net operating loss	23,094		—
Other	5,716		7,848
Total deferred tax assets	152,143		117,996
Deferred tax liabilities
Excess of tax over book depreciation	990,682		897,667
Purchased-gas cost adjustment	13,822		3,999
Other regulatory assets and liabilities, net	186,207		168,115
Total deferred tax liabilities	1,190,711		1,069,781
Net deferred tax liabilities	$	1,038,568	$	951,785