13. Income Taxes

Components of income tax expense (benefit) consist of the following (in thousands):

	Year Ended December 31,
	2015			2014			2013
Current:
Federal	$	320,726		$	137,993		$	120,030
State		33,978			19,051			20,099
Foreign		806			1,252			2,164

Total current		355,510			158,296			142,293
Deferred
Federal		(2,846	)		(2,945	)		(37,713	)
State		7,279			463			(9,059	)
Foreign		194			(225	)		(1,055	)

Total deferred		4,627			(2,707	)		(47,827	)


Other non-current
Federal		29,678			27,115			7,797
State		2,990			2,383			1,907
Foreign		(7	)		19			173

Total other		32,661			29,517			9,877


Total income tax expense	$	392,798		$	185,106		$	104,343

Presented below is a reconciliation of income taxes computed at the statutory federal tax rate to income tax expense as reported (in thousands):

	Year Ended December 31,
	2015			2014			2013
Federal tax provision computed at 35%	$	365,476		$	183,813		$	97,616
State tax provision, net of federal tax provision		28,760			12,865			8,320
General business credits		(6,904	)		(12,195	)		(13,346	)
Incentive stock option expense		—			(181	)		(304	)
Section 199 deduction		(21,774	)		(11,735	)		(10,861	)
Nondeductible compensation expense		29,280			13,000			22,813
Nondeductible expenses		(2,040	)		(461	)		105

Total income tax expense	$	392,798		$	185,106		$	104,343

Components of the net deferred tax asset are as follows (in thousands):

	As of December 31,
	2015			2014
Deferred tax assets:
General business credits	$	—		$	2,186
Impairment losses on investments		294			291
License fees capitalized for tax purposes		53,439			61,770
Nonqualified stock options		37,424			42,697
SERP		17,141			17,478
STAP awards		95,152			86,414
Other		27,074			29,086

Total deferred tax assets		230,524			239,922
Deferred tax liabilities:
Plant and equipment principally due to differences in depreciation		(26,461	)		(30,758	)
Other		(7,995	)		(7,854	)

Net deferred tax asset before valuation allowance		196,068			201,310
Valuation allowance		(3,392	)		(2,981	)

Net deferred tax assets	$	192,676		$	198,329

Deferred tax assets are reduced by a valuation allowance when, in our judgment, it is more likely than not that a portion or all of the deferred tax assets will not be realized. In evaluating our ability to realize deferred tax assets, we consider all available positive and negative evidence. Accordingly, we consider past operating results, forecasts of earnings and taxable income, the reversal of temporary differences and any prudent and feasible tax planning strategies. Future increases in the valuation allowance would result in a corresponding charge to earnings in the period such a determination is made. Conversely, future reductions to the valuation allowance would result in the recognition of a tax benefit in the period we conclude a reduction is warranted.

A reconciliation of the beginning and ending balances of unrecognized tax benefits for the years indicated is as follows (in thousands):

Unrecognized tax benefits at January 1, 2013	$	1,511
Gross increases—tax positions in prior period		1,325

Unrecognized tax benefits at December 31, 2013	$	2,836


Unrecognized tax benefits at January 1, 2014	$	2,836
Gross increases—tax positions in prior period		28
Gross decreases—tax positions in prior period		(1,419	)

Unrecognized tax benefits at December 31, 2014	$	1,445


Unrecognized tax benefits at January 1, 2015	$	1,445
Lapse of statute of limitations		(945	)

Unrecognized tax benefits at December 31, 2015	$	500

Included in unrecognized tax benefits at December 31, 2015, 2014 and 2013, is $342,000, $1.0 million, and $2.4 million, respectively, of tax benefits that, if recognized, would impact the effective tax rate. As of December 31, 2015 and 2014, we accrued zero and $28,000, respectively, in interest expense relating to uncertain state tax positions.

We are subject to federal and state taxation in the United States and various foreign jurisdictions. Currently, our 2014, 2013, 2012 and 2011 tax years are subject to examination by the IRS and by state taxing authorities. We are unaware of any positions for which it is reasonably possible that the total amounts of unrecognized tax benefits will significantly increase or decrease within the next twelve months.