	Year Ended December 31,
	2018			2017			2016
	(in thousands)
United States	$	(69,769	)	$	(54,894	)	$	(47,112	)
Foreign		7,809			4,855			2,083
Total	$	(61,960	)	$	(50,039	)	$	(45,029	)

	Year Ended December 31,
	2018			2017			2016
	(in thousands)
Current income tax provision
Federal	$	(184	)	$	—		$	—
State		(140	)		(144	)		(95	)
Foreign		(1,508	)		(1,077	)		(579	)
Total current income tax provision		(1,832	)		(1,221	)		(674	)
Deferred income tax benefit
Federal		21			10,435			61
State		—			977			—
Foreign		(57	)		134			80
Total deferred income tax benefit		(36	)		11,546			141
Total income tax benefit (provision)	$	(1,868	)	$	10,325		$	(533	)

The following reconciles the differences between income taxes computed at the federal statutory rate of 21% for 2018 and 35% for 2017 and 2016 and the provision for income taxes:

	Year Ended December 31,
	2018			2017			2016
	(in thousands)
Expected income tax benefit at the federal statutory rate	$	12,955		$	17,166		$	15,761
State taxes net of federal benefit		5,155			5,150			916
Stock-based compensation		17,575			10,939			(2,001	)
Difference in foreign tax rates		435			988			415
U.S. tax credits		1,763			1,717			1,609
Convertible debt and acquisition		—			11,573			—
Federal rate change		—			(49,123	)		—
Transition tax		—			(1,063	)		—
GILTI inclusion		(1,177	)		—			—
Meals & entertainment		(1,411	)		(745	)		(612	)
Change in valuation allowance		(37,059	)		13,988			(16,413	)
Other		(104	)		(265	)		(208	)
Income tax benefit (provision)	$	(1,868	)	$	10,325		$	(533	)

On December 22, 2017, the United States of America signed tax legislation (the “2017 Act”) which enacts a wide range of changes to the U.S. corporate income tax system. The 2017 Act reduces the U.S. corporate tax rate from 35% to 21% effective January 1, 2018, broadens the tax base and changes rules for expensing and capitalizing business expenditures, establishes a territorial tax system for foreign earnings as well as a minimum tax on certain foreign earnings, provides for a one-time transition tax on previously undistributed foreign earnings, and introduces new rules for the treatment of certain export sales.. The Company recorded provisional estimates for the impact of the 2017 Act during period ended December 31, 2017. The accounting for the 2017 Act is now complete and no significant adjustments were made 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,
	2018			2017
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	118,897		$	87,521
Research and investment credits		11,154			9,402
Accruals and reserves		7,734			6,627
Depreciation		1,119			911
Stock-based compensation		5,404			4,146
Interest expense		2,466			—
Total deferred tax assets		146,774			108,607
Deferred tax liabilities:
Intangible assets		(1,002	)		(1,273	)
Convertible debt		(4,675	)		(5,664	)
Capitalized costs		(8,002	)		(4,648	)
Total deferred tax liabilities		(13,679	)		(11,585	)
Valuation allowance		(132,759	)		(96,630	)
Net deferred tax assets	$	336		$	392

The Company reviews all available evidence to evaluate its recovery of deferred tax assets, including its recent history of accumulated losses in all tax jurisdictions 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 $36.1 million in 2018, $5.5 million in 2017 and $16.5 million in 2016, 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. At December 31, 2018, the Company has completed its accounting for the impact of the 2017 Act and has determined that it will no longer assert indefinite reinvestment of its foreign earnings. Through December 31, 2017, these earnings 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 year-ended December 31, 2018 have been subject to U.S. federal income tax via the newly enacted 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 $479.5 million and $301.4 million, respectively at December 31, 2018. 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 20 year carryforward period and will expire at various dates through 2037. State net operating losses will expire at various dates through 2038. The Company had a federal interest expense carryforward of $10.0 million at December 31, 2018 which has an indefinite carryforward period.

The Company had federal research and development credit carryforwards of $6.8 million at December 31, 2018 that expire at various dates through 2038. The Company also has state research and investment credit carryforwards of $3.5 million and $932 thousand, respectively that expire at various dates through 2033.

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, 2017, 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 2018. 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 the 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,
	2018		2017		2016
	(in thousands)
Unrecognized benefit—beginning of the year	$	2,725	$	1,742	$	673
Gross increases—current period positions		1,200		983		1,069
Gross decrease—prior period positions		—		—		—
Unrecognized benefit—end of period	$	3,925	$	2,725	$	1,742

All of the gross unrecognized tax benefits represent a reduction to the research and development tax credit carryforward.

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, 2018.

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, Ireland, Australia, Singapore, Japan, Germany, Colombia, Canada, Sweden and various state jurisdictions. 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 in Ireland for tax years 2014 through present. The Company also remains open to examination for varying periods in the other foreign jurisdictions. The Company is routinely examined by various taxing authorities. The IRS completed a federal income tax audit for the tax year 2013 during 2016. The completed federal income tax audit did not yield a material effect on the Company’s financial condition or results of operations.