The sources of income before income taxes for the years ended December 31, 2022, 2021 and 2020 are presented as follows:

The Company's income tax expense for the years ended December 31, 2022, 2021 and 2020 consisted of the following:

	Year Ended December 31,
(in thousands)	2022			2021			2020
Current tax expense (benefit):
U.S.	$	3,878		$	2,810		$	2,605
Foreign	80,296			59,874			39,270
Total current	84,174			62,684			41,875
Deferred tax expense (benefit):
U.S.	(7,270		)	12,269			(16,100		)
Foreign	14,949			(9,865		)	(14,300		)
Total deferred	7,679			2,404			(30,400		)
Total tax expense	$	91,853		$	65,088		$	11,475

The following is a reconciliation of the federal statutory income tax rates of 21% to the effective income tax rate for the years ended December 31, 2022, 2021 and 2020:

	Year Ended December 31,
(dollar amounts in thousands)	2022			2021			2020
U.S. federal income tax expense at applicable statutory rate	$	67,745		$	28,492		$	1,716
Tax effect of:
State income tax expense at statutory rates, net of U.S. federal income tax	3,666			1,516			347
Non-deductible expenses	1,698			538			1,887
Share-based compensation	1,930			(3,524		)	(6,446		)
Other permanent differences	(219		)	(2,047		)	3,828
Difference between U.S. federal and foreign tax rates	13,859			7,438			7,002
Provision in excess of statutory rates	3,592			2,879			(6,491		)
Change in federal and foreign valuation allowance	(7,704		)	26,673			(4,238		)
Impairment of goodwill and acquired intangibles assets	—			—			22,053
GILTI, net of tax credits	9,807			3,900			—
Tax credits	(697		)	(1,122		)	(3,518		)
Other	(1,824		)	345			(4,665		)
Total income tax expense	$	91,853		$	65,088		$	11,475
Effective tax rate	28.47		%	48.0		%	140.4		%

We calculate our provision for federal, state and foreign income taxes based on current tax law.

The tax effect of temporary differences and carryforwards that give rise to deferred tax assets and liabilities from continuing operations are as follows:

	As of December 31,
(in thousands)	2022			2021
Deferred tax assets:
Tax loss carryforwards	$	64,889		$	65,862
Share-based compensation	12,620			9,743
Accrued expenses	23,192			19,907
Property and equipment	10,787			11,949
Goodwill and intangible amortization	8,999			9,353
Contract costs	7,034			9,921
Intercompany notes	17,352			6,077
Accrued revenue	5,073			7,541
Tax credits	64,384			65,267
Lease accounting	40,194			42,381
Foreign exchange	2,704			8,283
Other	7,755			14,616
Total deferred tax assets	264,983			270,900
Valuation allowance	(90,369		)	(100,489		)
Total deferred tax assets, net of valuation allowance	174,614			170,411
Deferred tax liabilities:
Intangible assets related to purchase accounting	(12,067		)	(11,763		)
Goodwill and intangible amortization	(31,716		)	(30,339		)
Accrued expenses	(22,661		)	(21,495		)
Intercompany notes	(14,544		)	(10,388		)
Accrued interest	(26,583		)	(34,175		)
Capitalized research and development	(1,229		)	(6,376		)
Property and equipment	(14,630		)	(15,597		)
Accrued revenue	(2,074		)	(2,073		)
Lease accounting	(40,194		)	(42,381		)
Foreign exchange	(9,773		)	(1,211		)
Other	(3,533		)	(3,971		)
Total deferred tax liabilities	(179,004		)	(179,769		)
Net deferred tax liabilities	$	(4,390	)	$	(9,358	)

Net deferred tax assets of $24.0 million and $36.8 million as of December 31, 2022 and 2021, respectively, are recorded within "Other assets" on the Consolidated Balance Sheet.

Subsequently recognized tax benefits relating to the valuation allowance for deferred tax assets as of December 31, 2022 are expected to be allocated to income taxes in the Consolidated Statements of Operations. As of December 31, 2022, and 2021, the Company's foreign tax loss carryforwards were $260.6 million and $267.3 million, respectively, and U.S. state tax loss carryforwards were $97.7 million and $73.7 million, respectively.

As of December 31, 2022, the Company had U.S. foreign tax credit carryforwards of $59.8 million which are largely not expected to be utilized in future periods. As of December 31, 2021, the Company had 100 U.S. foreign tax credit carryforwards of $61.6 million which are largely not expected to be utilized in future periods.

In assessing the Company's ability to realize 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 upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considers the scheduled reversal of deferred tax liabilities, projected future taxable income and tax planning strategies in making this assessment. Based upon the level of historical taxable income and projections for future taxable income over the periods in which the deferred tax assets are deductible, management believes it is more likely than not the Company will realize the benefits of these deductible differences, net of the existing valuation allowances, as of December 31, 2022.

As of December 31, 2022, the Company had foreign tax net operating loss carryforwards of $260.6 million, which will expire as follows:

(in thousands)	Gross		Tax Effected
Year ending December 31,
2023	$	2,244	$	516
2024	2,247		503
2025	16,533		3,872
2026	17,655		4,106
2027	4,781		1,151
Thereafter	18,904		4,941
Unlimited	198,253		46,293
Total	$	260,617	$	61,382

In addition, the Company's state tax net operating loss carryforwards of $97.7 million will expire periodically from 2023 through 2042, U.S. foreign tax credit carryforwards of $59.8 million will expire periodically from 2023 through 2032 and U.S. federal research and expenditure credit carryforwards of $3.8 million will expire periodically from 2034 through 2041.

The Company has not provided additional deferred taxes with respect to items such as certain foreign exchange gains or losses, foreign withholding taxes or additional state taxes, if any, on undistributed earnings attributable to foreign subsidiaries and it is not practical to determine the income tax liability that would be payable if such earnings were not reinvested indefinitely. Gross undistributed earnings reinvested indefinitely in foreign subsidiaries aggregated approximately $2,063.1 million as of December 31, 2022.

Accounting for uncertainty in income taxes

A reconciliation of the beginning and ending amount of unrecognized tax benefits for the years ended December 31, 2022 and 2021 is as follows:

	Year Ended December 31,
(in thousands)	2022			2021
Beginning balance	$	40,990		$	39,785
Additions based on tax positions related to the current year	6,125			3,815
Additions for tax positions of prior years	258			—
Reductions for tax positions of prior years	(3,971		)	(1,998		)
Settlements	(586		)	—
Statute of limitations expiration	—			(612		)
Ending balance	$	42,816		$	40,990

As of December 31, 2022 and 2021, approximately $30.8 million and $29.1 million, respectively, of the unrecognized tax benefits would impact the Company's provision for income taxes and effective income tax rate, if recognized. Total estimated accrued interest and penalties related to the underpayment of income taxes was $8.3 million and $7.2 million as of December 31, 2022 and 2021, respectively. The following income tax years remain open in the Company's major jurisdictions as of December 31, 2022:

Jurisdictions	Periods
U.S. (Federal)	2014 through 2022
Germany	2016 through 2022
Greece	2013 through 2022
Spain	2015 through 2022
U.K.	2018 through 2022

It is reasonably possible that the balance of gross unrecognized tax benefits could significantly change within the next twelve months as a result of the resolution of audit examinations and expirations of certain statutes of limitations and, accordingly, materially affect the Company's operating results. At this time, it is not possible to estimate the range of change due to the uncertainty of potential outcomes.