|6 Months Ended|
Jun. 30, 2019
|Income Tax Disclosure [Abstract]|
We file an income tax return in the U.S. federal jurisdiction and a margin tax return in Texas. We received notification from the Internal Revenue Service ("IRS") in November 2016 that the December 31, 2014, tax return was selected for audit. In April 2017, the audit was expanded to include the year ended December 31, 2015, to review the refund claim related to research and development activities. We received notification from the IRS in March 2018 that the audit was complete. We also received notification that Texas will audit our R&D credit calculations for 2014 and 2015. We were notified by Texas that the audit has been temporarily suspended as the Comptroller's office reviews its audit process regarding R&D credits. We do not expect any changes related to the Texas audit. Tax returns for various jurisdictions remain open for examination for the years 2014 through 2018. As of June 30, 2019 and December 31, 2018, respectively, we recognized no adjustment for uncertain tax positions or related interest and penalties.
The effective tax rate varies from the federal statutory rate of 21%, primarily as a result of state tax expense, stock based compensation and a research and development credit for the three and six months ended June 30, 2019 and 2018. We continue to maintain a valuation allowance against certain deferred tax assets, specifically for mining claims for PEVM, where realization is not certain.
The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef