	Year Ended December 31,
	2019			2018			2017
	(in thousands)
United States	$	(63,200	)	$	(69,769	)	$	(54,894	)
Foreign		12,427			7,809			4,855
Total	$	(50,773	)	$	(61,960	)	$	(50,039	)

	Year Ended December 31,
	2019			2018			2017
	(in thousands)
Current income tax provision
Federal	$	(238	)	$	(184	)	$	—
State		(241	)		(140	)		(144	)
Foreign		(3,293	)		(1,508	)		(1,077	)
Total current income tax provision		(3,772	)		(1,832	)		(1,221	)
Deferred income tax benefit
Federal		160			21			10,435
State		—			—			977
Foreign		639			(57	)		134
Total deferred income tax benefit (expense)		799			(36	)		11,546
Total income tax benefit (provision)	$	(2,973	)	$	(1,868	)	$	10,325

The following reconciles the differences between income taxes computed at the federal statutory rate of 21% for 2019 and 2018 and 35% for 2017 and the provision for income taxes:

	Year Ended December 31,
	2019			2018			2017
	(in thousands)
Expected income tax benefit at the federal statutory rate	$	10,665		$	12,955		$	17,166
State taxes net of federal benefit		3,700			5,155			5,150
Stock-based compensation		16,055			17,575			10,939
Executive compensation limitation		(7,244	)		—			—
Difference in foreign tax rates		693			435			988
U.S. tax credits		24,170			1,763			1,717
Convertible debt and acquisition		—			—			11,573
Federal rate change		—			—			(49,123	)
Transition tax		—			—			(1,063	)
GILTI inclusion		(1,645	)		(1,177	)		—
Meals and entertainment		(1,208	)		(1,411	)		(745	)
Change in valuation allowance		(47,523	)		(37,059	)		13,988
Other		(636	)		(104	)		(265	)
Income tax benefit (provision)	$	(2,973	)	$	(1,868	)	$	10,325

On December 22, 2017, the United States of America signed tax legislation (the “2017 Act”) which enacted a wide range of changes to the U.S. corporate income tax system. The 2017 Act reduced the U.S. corporate tax rate from 35% to 21% effective January 1, 2018, broadened the tax base and changes rules for expensing and capitalizing business expenditures, established a territorial tax system for foreign earnings as well as a minimum tax on certain foreign earnings, provided for a one-time transition tax on previously undistributed foreign earnings, and introduced new rules for the treatment of certain export sales. The Company recorded provisional estimates for the impact of the 2017 Act during the period ended December 31, 2017 and completed the accounting in 2018 without any significant adjustments to the provisional estimates.

Deferred Tax Assets and Liabilities —Deferred income taxes reflect the net effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets and liabilities were as follows:

	Year Ended December 31,
	2019			2018
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	142,512		$	118,897
Research and investment credits		35,285			11,154
Accruals and reserves		9,239			7,734
Depreciation		1,756			1,119
Stock-based compensation		5,451			5,404
Interest expense		3,197			2,466
Total deferred tax assets		197,440			146,774
Deferred tax liabilities:
Intangible assets		(2,678	)		(1,002	)
Convertible debt		(3,550	)		(4,675	)
Capitalized costs		(11,351	)		(8,002	)
Depreciation		(138	)		—
Total deferred tax liabilities		(17,717	)		(13,679	)
Valuation allowance		(180,092	)		(132,759	)
Net deferred tax assets	$	(369	)	$	336

The Company reviews all available evidence to evaluate the realizability of its deferred tax assets, including its recent history of accumulated losses over the most recent three years as well as its ability to generate income in future periods. The Company has provided a valuation allowance against its U.S. net deferred tax assets as it is more likely than not that these assets will not be realized given the nature of the assets and the likelihood of future utilization.

The valuation allowance increased by $47.3 million in 2019, $36.1 million in 2018 and $5.5 million in 2017, primarily due to the increase in the U.S. net operating loss deferred tax asset. The Company does not expect any significant changes in its valuation allowance positions within the next 12 months.

Prior to the 2017 Act, the Company had asserted that the earnings of its foreign subsidiaries were indefinitely reinvested in the operations of those subsidiaries. In 2018, the Company completed its accounting for the impact of the 2017 Act and determined that it would no longer assert indefinite reinvestment of its foreign earnings. Earnings through December 31, 2017 have been subject to U.S. federal income tax via the one-time transition tax on previously undistributed foreign earnings. The foreign earnings for the years ended December 31, 2019 and 2018 have been subject to U.S. federal income tax via the Global Intangible Low-Taxed Income (“GILTI”) provision. The Company has determined that any incremental tax incurred upon ultimate distribution of these earnings to the U.S. would not be material.

The Company had federal and state net operating loss carryforwards of $947 million at December 31, 2019 and $781 million at December 31, 2018. The Company also had international net operating loss carryforwards of $6 million at December 31, 2019. As a result of the 2017 Act all federal net operating losses, created after January 1, 2018, have an indefinite carryforward period. All federal net operating losses, created before January 1, 2018, are subject to a 20 year carryforward period and will expire at various dates through 2037. State net operating losses will expire at various dates through 2039. The Company has a federal interest expense carryforward of $13.0 million at December 31, 2019, and $10.0 million at December 31, 2018, which have an indefinite carryforward period.

The Company had federal research and development credit carryforwards of $23.0 million at December 31, 2019 that expire at various dates through 2039. The Company also has state research and investment tax credit carryforwards of $12.2 million, that expire at various dates through 2034.

Under Section 382 of the Internal Revenue Code of 1986, as amended, substantial changes in the Company's ownership may limit the amount of net operating loss carryforwards that could be utilized annually in the future to offset taxable income. Specifically, this limitation may arise in the event of a cumulative change in ownership of the Company of more than 50% within a three-year period. Any such annual limitation may significantly reduce the utilization of net operating loss carryforwards before they expire. The Company performed an analysis through December 31, 2018 and determined any potential ownership change under Section 382 during the year would not have a material impact on the future utilization of US net operating losses and tax credits. There was no material change to this conclusion in 2019. However, future transactions in the Company's common stock could trigger an ownership change for purposes of Section 382, which could limit the amount of net operating loss carryforwards and other attributes that could be utilized annually in the future to offset taxable income, if any. Any such limitation, whether as the result of sales of common stock by our existing stockholders or sales of common stock by the Company, could have a material adverse effect on results of operations in future years.

Uncertain Tax Positions —The Company accounts for uncertainty in income taxes using a two-step process. The Company first determines whether it is more likely than not that a tax position will be sustained upon examination by a tax authority, including resolutions of any related appeals or litigation processes, based on technical merit. If a tax position meets the more-likely-than-not recognition threshold it is then measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement.

	Year Ended December 31,
	2019			2018		2017
	(in thousands)
Unrecognized benefit—beginning of the year	$	3,925		$	2,725	$	1,742
Gross increases—current period positions		2,387			1,200		983
Gross decrease—prior period positions		(867	)		—		—
Unrecognized benefit—end of period	$	5,445		$	3,925	$	2,725

All of the gross unrecognized tax benefits represent a reduction to the research and development tax credit carryforward. The gross decrease to prior period positions is a result of the Company completing its documentation of credits generated between 2015 and 2018.

All of the unrecognized tax benefits decrease deferred tax assets with a corresponding decrease to the valuation allowance. None of the unrecognized tax benefits would affect the Company’s effective tax rate if recognized in the future.

The Company has elected to recognize interest and penalties related to uncertain tax positions as a component of income tax expense. No interest or penalties have been recorded through December 31, 2019 because the Company has no tax due because of significant NOL carryforwards.

The Company does not expect any significant change in its unrecognized tax benefits within the next 12 months.

The Company files tax returns in the United States and various jurisdictions throughout the world where the Company has operations or established a taxable presence. All of the Company’s tax years remain open to examination in the United States, as carryforward attributes generated in past years may still be adjusted upon examination by the Internal Revenue Service or state tax authorities if they have or will be used in future periods. The Company remains open to examination for varying periods in the other foreign jurisdictions and is routinely examined by various taxing authorities.