Income Taxes	6 Months Ended
Jun. 29, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for income taxes is determined using an estimated annual effective tax rate, which is generally less than the U.S. federal statutory rate, primarily due to research and development (“R&D”) tax credits. Our effective tax rate may be subject to fluctuations during the year as new information is obtained, which may affect the assumptions used to estimate the annual effective tax rate, including factors such as expected utilization of R&D tax credits, valuation allowances against deferred tax assets, the recognition or derecognition of tax benefits related to uncertain tax positions, and changes in or the interpretation of tax laws in jurisdictions where we conduct business. Also, excess tax benefits and tax deficiencies related to our equity compensation recognized in the income statement could result in fluctuations in our effective tax rate period-over-period depending on the volatility of our stock price and how many awards vest in the period. We recognize deferred tax assets and liabilities for temporary differences between the financial reporting basis and the tax basis of our assets and liabilities along with net operating loss and tax credit carryovers. We record a valuation allowance against our deferred tax assets to reduce the net carrying value to an amount that we believe is more likely than not to be realized. When we establish or reduce our valuation allowances against our deferred tax assets, the provision for income taxes will increase or decrease, respectively, in the period when that determination is made. We recorded income tax expense of $1.4 million for the three months ended June 29, 2019 compared to $0.2 million for the three months ended June 30, 2018. The increase in income tax expense for the second quarter of 2019 compared to the second quarter of 2018 was primarily due to higher pre-tax income for the second quarter of 2019 compared to the second quarter of 2018. The increase in income tax expense was partially offset by higher discrete tax benefits recognized in the second quarter of 2019 for net tax windfalls related to stock-based compensation and changes in deferred tax assets and liabilities due to state tax laws enacted in the period. We recorded income tax expense of $2.4 million for the six months ended June 29, 2019 compared to an income tax benefit of less than $0.1 million for the six months ended June 30, 2018. The increase in income tax expense for the first six months of 2019 compared to the first six months of 2018 was primarily due to higher pre-tax income for the first six months of 2019 compared to the first six months of 2018. The increase in income tax expense was partially offset by higher discrete tax benefits recognized in the first six months of 2019 for net tax windfalls related to stock-based compensation and changes in deferred tax assets and liabilities due to state tax laws enacted in the period. Our total amount of unrecognized tax benefits was $5.4 million and $5.3 million as of June 29, 2019 and December 31, 2018, respectively. If recognized, $3.5 million would affect the effective tax rate. We do not reasonably expect significant increases or decreases to our unrecognized tax benefits in the next twelve months.

Income Taxes

The provision for income taxes is determined using an estimated annual effective tax rate, which is generally less than the U.S. federal statutory rate, primarily due to research and development (“R&D”) tax credits. Our effective tax rate may be subject to fluctuations during the year as new information is obtained, which may affect the assumptions used to estimate the annual effective tax rate, including factors such as expected utilization of R&D tax credits, valuation allowances against deferred tax assets, the recognition or derecognition of tax benefits related to uncertain tax positions, and changes in or the interpretation of tax laws in jurisdictions where we conduct business. Also, excess tax benefits and tax deficiencies related to our equity compensation recognized in the income statement could result in fluctuations in our effective tax rate period-over-period depending on the volatility of our stock price and how many awards vest in the period. We recognize deferred tax assets and liabilities for temporary differences between the financial reporting basis and the tax basis of our assets and liabilities along with net operating loss and tax credit carryovers.

We record a valuation allowance against our deferred tax assets to reduce the net carrying value to an amount that we believe is more likely than not to be realized. When we establish or reduce our valuation allowances against our deferred tax assets, the provision for income taxes will increase or decrease, respectively, in the period when that determination is made.

We recorded income tax expense of $1.4 million for the three months ended June 29, 2019 compared to $0.2 million for the three months ended June 30, 2018. The increase in income tax expense for the second quarter of 2019 compared to the second quarter of 2018 was primarily due to higher pre-tax income for the second quarter of 2019 compared to the second quarter of 2018. The increase in income tax expense was partially offset by higher discrete tax benefits recognized in the second quarter of 2019 for net tax windfalls related to stock-based compensation and changes in deferred tax assets and liabilities due to state tax laws enacted in the period.

We recorded income tax expense of $2.4 million for the six months ended June 29, 2019 compared to an income tax benefit of less than $0.1 million for the six months ended June 30, 2018. The increase in income tax expense for the first six months of 2019 compared to the first six months of 2018 was primarily due to higher pre-tax income for the first six months of 2019 compared to the first six months of 2018. The increase in income tax expense was partially offset by higher discrete tax benefits recognized in the first six months of 2019 for net tax windfalls related to stock-based compensation and changes in deferred tax assets and liabilities due to state tax laws enacted in the period.

Our total amount of unrecognized tax benefits was $5.4 million and $5.3 million as of June 29, 2019 and December 31, 2018, respectively. If recognized, $3.5 million would affect the effective tax rate. We do not reasonably expect significant increases or decreases to our unrecognized tax benefits in the next twelve months.