We recorded an income tax provision of approximately $5.4 million, $2.6 million and $1.4 million for the years ended December 31, 2020, 2019 and 2018, respectively. The income tax provision for the years ended December 31, 2020, 2019 and 2018 was primarily due to state and foreign income tax expense.


	Years Ended December 31,
	2020		2019		2018
Current income taxes:
Federal	$	—	$	(185)	$	(91)
State	459		264		(73)
Foreign	5,010		2,594		1,374
Total current income taxes	5,469		2,673		1,210

Deferred income taxes:
Federal	187		(17)		155
State	255		42		76
Foreign	(551)		(64)		(11)
Total deferred income taxes	(109)		(39)		220
Total income tax provision	$	5,360	$	2,634	$	1,430


	Years Ended December 31,
	2020		2019		2018
United States	$	(10,369)	$	(12,497)	$	(18,617)
Foreign	9,508		5,526		5,159
Total	$	(861)	$	(6,971)	$	(13,458)

The differences between our income tax provision as presented in the accompanying consolidated statements of operations and the income tax expense computed at the federal statutory rate consists of the items shown in the following table as a percentage of pretax loss (in percentages):


	Years Ended December 31,
	2020		2019		2018
Income tax at U.S. statutory rate	21.0	%	21.0	%	21.0	%
State, net of federal benefit	(169.5)		(76.3)		14.8
Foreign rate differential	(285.9)		(19.4)		(3)
Share-based compensation	2,901.5		695.4		178.7
Non-deductible expenses	(50.3)		0.4		(4.4)
Tax credits	351.6		19.3		26.7

Acquisition related	—		31.8		15.2
Convertible senior notes	(5,854.8)		(412.6)		(0.3)
Other	1.2		27.9		(1.8)
Change in valuation allowance	2,462.7		(325.3)		(257.5)
Total	(622.5)	%	(37.8)	%	(10.6)	%


	As of December 31,
	2020		2019
Deferred tax assets:
Accrued expenses and reserves	$	6,365	$	3,978
Share-based compensation	6,473		12,003
Accrued compensation	2,402		997
Net operating loss carryforwards	190,904		162,320

Other items	5,734		3,438
Gross deferred tax assets	211,878		182,736
Valuation allowance	(151,825)		(148,519)
Total deferred tax assets	60,053		34,217

Deferred tax liabilities:
Property and equipment, textbooks and intangibles assets	(4,066)		(4,111)
Convertible senior notes	(51,607)		(27,065)
Other	(5,890)		(4,661)
Total deferred tax liabilities	(61,563)		(35,837)

Net deferred tax liability	$	(1,510)	$	(1,620)

At December 31, 2020 and 2019, the deferred tax liability is primarily created by the tax amortization of acquired indefinite lived intangible assets. Under the accounting guidance this deferred tax liability can be used as a source of income for recognition of deferred tax assets when determining the amount of valuation allowance to be recorded.

As of December 31, 2020, we intend to permanently reinvest all 2020, 2019, and 2018 earnings from our foreign subsidiaries. As such, we have not provided for any remaining tax effect, if any, of the outside basis difference of our foreign subsidiaries based upon plans of future reinvestment. The determination of the future tax consequences of the remittance of these earnings is not practicable.

Realization of the deferred tax assets is dependent upon future taxable income, the amount and timing of which are uncertain. Accordingly, the federal and state gross deferred tax assets have been fully offset by a valuation allowance. The

valuation allowance increased by approximately $3.3 million during the year ended December 31, 2020 and increased by approximately $22.7 million during the year ended December 31, 2019.

As of December 31, 2020, we had net operating loss carryforwards for federal and state income tax purposes of approximately $674 million and $511 million, respectively, which will begin to expire in years beginning 2028 and 2021, respectively.

As of December 31, 2020, we had tax credit carryforwards for federal and state income tax purposes of approximately $19.1 million and $14.8 million, respectively. The federal credits expire in various years beginning in 2030. The state credits do not expire.

Utilization of our net operating losses and tax credit carryforwards may be subject to substantial annual limitations due to ownership change limitations provided by the Internal Revenue Code of 1986, as amended (IRC), and similar state provisions. Such annual limitations could result in the expiration of the net operating losses and tax credit carryforwards before utilization.

We recognize interest and penalties related to uncertain tax positions as a component of income tax expense. During the years ended December 31, 2020, 2019 and 2018, we recognized an increase of $0.1 million, an increase of $45 thousand and a decrease of $0.7 million of interest and penalties, respectively. Accrued interest and penalties as of December 31, 2020 and 2019 were approximately $0.2 million and $0.1 million, respectively.

We file tax returns in U.S. federal, state, and certain foreign jurisdictions with varying statutes of limitations. Due to net operating loss and credit carryforwards, all of the tax years since inception through the 2020 tax year remain subject to examination by the U.S. federal and some state authorities. Foreign jurisdictions remain subject to examination up to approximately seven years from the filing date, depending on the jurisdiction.

A reconciliation of the beginning and ending balances of the total amount of unrecognized tax benefits, excluding accrued interest and penalties, is as follows (in thousands):


	Years Ended December 31,
	2020		2019		2018
Beginning balance	$	10,993	$	8,771	$	5,772
Increase in tax positions for prior years	479		221		758
Decrease in tax positions for prior years	(535)		(1,550)		(569)
Decrease in tax positions for prior year settlement	(208)		—		(149)
Decrease in tax positions for prior years due to statutes lapsing	(26)		(164)		(103)
Increase in tax positions for current year	3,999		3,722		3,112
Change due to translation of foreign currencies	(48)		(7)		(50)
Ending balance	$	14,654	$	10,993	$	8,771

The amount of unrecognized tax benefits, if recognized, that would affect the effective tax rate is $3.4 million for the year ended December 31, 2020. One or more of these unrecognized tax benefits could be subject to a valuation allowance if, and when recognized in a future period, which could impact the timing of any related effective tax rate benefit.