	Year ended December 31,
	2020		2019		2018
United States	$	38,839	$	53,629	$	13,565
Foreign		124,690		116,276		50,746
Income before income taxes	$	163,529	$	169,905	$	64,311

	Year ended December 31,
	2020			2019			2018
Current income tax (expense) benefit:
Federal	$	(14,773	)	$	(20,108	)	$	(9,097	)
State		(568	)		(755	)		(511	)
Foreign		(19,262	)		(16,514	)		(8,677	)
		(34,603	)		(37,377	)		(18,285	)
Deferred income tax (expense) benefit:
Federal		4,883			5,208			12,622
State		(34	)		1,054			611
Foreign		(403	)		(486	)		(419	)
		4,446			5,776			12,814
Income tax expense	$	(30,157	)	$	(31,601	)	$	(5,471	)

Reconciliation of the statutory U.S. federal tax rate to the Company's effective tax rate is as follows:

	Year ended December 31,
	2020			2019			2018
Statutory U.S. federal income tax rate		21.0	%		21.0	%		21.0	%
State income taxes, net of federal benefit		0.2			0.1			(0.2	)
Effect of foreign operations		(5.2	)		(5.4	)		(4.7	)
Accruals and reserves		(1.0	)		(1.1	)		—
Nondeductible employee compensation		2.6			2.5			1.7
Research tax credits		(1.8	)		(1.4	)		(2.7	)
Stock based compensation		(0.9	)		(1.7	)		(2.7	)
U.S. Tax Cuts and Jobs Act		—			—			(3.5	)
U.S. International Tax (Sub F, GILTI, FDII)		3.5			3.8			(1.2	)
Other		—			0.8			0.8
Effective tax rate		18.4	%		18.6	%		8.5	%

The following table summarizes Company tax credit carry forwards for tax return purposes at December 31, 2020 (in thousands):

Significant components of the Company's net deferred tax assets and liabilities are as follows (in thousands):

	December 31,
	2020			2019
Deferred tax asset:
Capitalized technology license and patents	$	580		$	560
Capitalized research expenditures		4,291			3,319
Accruals and reserves		4,178			4,130
Retirement plan		15,444			11,363
Deferred revenue		16,834			14,354
Tax credit carry forwards		4,589			3,997
Stock-based compensation		1,059			1,884
Other		1,914			1,682
		48,889			41,289
Valuation allowance		(4,560	)		(3,368	)
Deferred tax assets		44,329			37,921
Deferred tax liability:
Accruals and reserves		(6,634	)		(7,546	)
Deferred tax liabilities		(6,634	)		(7,546	)
Net deferred tax assets	$	37,695		$	30,375

In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent on the Company's ability to generate future taxable income to obtain benefit from the reversal of temporary differences, net operating loss carryforwards and tax credits. As part of its assessment, management considers the scheduled reversal of deferred tax liabilities, projected future taxable income, and tax planning strategies. At this time there is no evidence to release the valuation allowance that has historically been recorded for the New Jersey research and development credit.

On December 27, 2018, the Korean Supreme Court, citing prior cases, held that the applicable law and interpretation of the Korea-U.S. Tax Treaty were clear that only royalties paid with respect to Korean registered patents are Korean source income and subject to Korean withholding tax. Based on this decision, the Company has decided to litigate the Korean withholding taxes paid or withheld on the 2018, 2019 and 2020 royalty payments and has engaged a leading Korean law firm which has advised that there is a more-likely-than-not chance of success. As a result, as of December 31, 2020 and 2019, the Company has recorded a long-term asset of $40.1 million and $26.9 million, respectively, representing the allocation of withholding to non-Korean patents and a long-term liability of $32.7 million and $25.7 million, respectively, for estimated amounts due to the U.S. Federal government based on the amendment of U.S. tax returns for lower withholding amounts.

With respect to the Korean withholding for the years 2011 through 2017, the Company has decided to continue the U.S.-Korean Mutual Agreement Procedure which was accepted by the Korean National Tax Service (KNTS) on September 15, 2017. The Company believes that it is more-likely-than-not that a favorable settlement will be reached resulting in a reduction of the Korean withholding taxes previously withheld since 2011. A long-term asset of $36.9 million for estimated refunds due from the Korean government, a long-term payable of $16.2 million for estimated amounts due to the U.S. Federal government based on amendment of prior year U.S. tax returns for the lower withholding amounts, and a reduction of deferred tax assets for foreign tax credits and research and development credits of $20.7 million has been recorded on the December 31, 2020 and 2019 Consolidated Balance Sheets for this matter.

On October 30, 2018, the KNTS concluded a tax audit with LG Display that included the licensing and royalty payments made to UDC Ireland during the years 2015 through 2017. The KNTS questioned whether UDC Ireland was the beneficial owner of these payments and assessed UDC Ireland a charge of $13.2 million for withholding and interest for the three-year period. UDC Ireland has engaged a leading Korean law firm which believes it is more-likely-than-not that UDC Ireland has beneficial ownership of the underlining intellectual property. Based on this authority, UDC Ireland has paid the assessment which is recorded as a long-term asset as of December 31, 2020 and 2019. In September 2020, the Korean District Court ruled entirely in the favor of UDC Ireland on the beneficial ownership issue. However, the KNTS has decided to appeal the ruling to the Korean High Court.

The Company has incurred Korean withholding tax of $14.9 million for each of the years ended December 31, 2020, 2019 and 2018, which will be appealed based on the interpretation of the Korea-U.S. Tax Treaty and recent Korean Supreme Court decisions.

The Company’s federal income tax returns for the years 2017 to 2020 are open and subject to examination. The State of New Jersey is currently auditing the 2014 to 2017 tax returns of UDC, Inc. The state and foreign tax returns are open for a period of generally three to four years.