In order to determine the quarterly provision for income taxes, the Company uses an estimated annual effective tax rate (“ETR”), which is based on expected annual income and statutory tax rates in the various jurisdictions. However, to the extent that application of the estimated annual effective tax rate is not representative of the quarterly portion of actual tax expense expected to be recorded for the year, the Company determines the provision for income taxes based on actual year-to-date income (loss). Certain significant or unusual items are separately recognized as discrete items in the period during which they occur and can be a source of variability in the effective tax rates from quarter to quarter.

The following table presents the Company’s income tax expense and effective income tax rate:

	Three Months Ended
	March 31,
	2021			2020
	(in thousands)
Income tax expense (benefit)	$	2,766		$	(1,824	)
Effective income tax rate		23.8	%		33.9	%

Income tax expense for the three months ended March 31, 2021 was $2.8 million at an effective tax rate of 23.8%. Income tax benefit for the three months ended March 31, 2020 was $1.8 million at an effective tax rate of 33.9%. The effective tax rate for the three months ended March 31, 2021 was primarily impacted by the tax effect of disallowed compensation and state income tax expense, offset by benefits on stock option exercises.

The Company is subject to income taxes domestically and in various foreign jurisdictions. Significant judgment is required in evaluating uncertain tax positions and determining the provision for income taxes.

The Company recognizes only those tax positions that meet the more-likely-than-not recognition threshold and establishes tax reserves for uncertain tax positions that do not meet this threshold. Interest and penalties associated with income tax matters are included in the provision for income taxes in the condensed consolidated statements of operations. As of March 31, 2021, the Company had uncertain tax positions of $3.9 million, inclusive of $0.8 million of interest and penalties.

The Company files U.S., state and foreign income tax returns in jurisdictions with various statutes of limitations. The federal tax years open under the statute of limitations are 2017 through 2019, and the state tax years open under the statute of limitations are 2016 through 2019.

The Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) was enacted in March 2020. The CARES Act includes several U.S. income tax provisions related to, among other things, net operating loss carrybacks, alternative minimum tax credits, modifications to the net interest deduction limitations, and technical amendments regarding the income tax depreciation of qualified improvement property placed in service after December 31, 2017. The CARES Act is not expected to have a material impact on the Company’s financial results.