Income Taxes	3 Months Ended
Mar. 31, 2019
Income Taxes [Abstract]
Income Taxes	6. Income Taxes Income Tax Expense Our effective income tax rate was a benefit of 82% and 44% for the three months ended March 31, 2019 and 2018, respectively. Our income tax rate for the three months ended March 31, 2019 increased primarily due to excess tax benefit deductions related to stock compensation. The income tax rate was favorably impacted by the research and development tax credit and losses in high rate jurisdictions, partially offset by unfavorable impacts of non-deductible operating expenses and executive compensation expenses. Our income tax rate for the three months ended March 31, 2018 was favorably impacted by losses in high rate jurisdictions and excess tax benefit deductions related to stock compensation, partially offset by unfavorable impacts of non-deductible operating expenses and executive compensation expenses. Deferred Income Taxes We generate deferred tax assets primarily as a result of write-downs of inventory and deferred preservation costs, accruals for product and tissue processing liability claims, investment and asset impairments, and operating losses. We acquired significant deferred tax assets, primarily net operating loss carryforwards, from our acquisitions of JOTEC GmbH (“JOTEC”) and its subsidiaries in 2017, On-X in 2016, Hemosphere, Inc. in 2012, and Cardiogenesis Corporation in 2011. We believe utilization of these net operating losses will not have a material impact on income taxes for the 2019 tax year. As of March 31, 2019 we maintained a total of $3.4 million in valuation allowances against deferred tax assets, primarily related to state net operating loss carryforwards, and had a net deferred tax liability of $22.2 million. As of December 31, 2018 we had a total of $3.4 million in valuation allowances against deferred tax assets, primarily related to state net operating loss carryforwards, and a net deferred tax liability of $23.2 million.

6. Income Taxes

Income Tax Expense

Our effective income tax rate was a benefit of 82% and 44% for the three months ended March 31, 2019 and 2018, respectively. Our income tax rate for the three months ended March 31, 2019 increased primarily due to excess tax benefit deductions related to stock compensation. The income tax rate was favorably impacted by the research and development tax credit and losses in high rate jurisdictions, partially offset by unfavorable impacts of non-deductible operating expenses and executive compensation expenses.

Our income tax rate for the three months ended March 31, 2018 was favorably impacted by losses in high rate jurisdictions and excess tax benefit deductions related to stock compensation, partially offset by unfavorable impacts of non-deductible operating expenses and executive compensation expenses.

Deferred Income Taxes

We generate deferred tax assets primarily as a result of write-downs of inventory and deferred preservation costs, accruals for product and tissue processing liability claims, investment and asset impairments, and operating losses. We acquired significant deferred tax assets, primarily net operating loss carryforwards, from our acquisitions of JOTEC GmbH (“JOTEC”) and its subsidiaries in 2017, On-X in 2016, Hemosphere, Inc. in 2012, and Cardiogenesis Corporation in 2011. We believe utilization of these net operating losses will not have a material impact on income taxes for the 2019 tax year.

As of March 31, 2019 we maintained a total of $3.4 million in valuation allowances against deferred tax assets, primarily related to state net operating loss carryforwards, and had a net deferred tax liability of $22.2 million. As of December 31, 2018 we had a total of $3.4 million in valuation allowances against deferred tax assets, primarily related to state net operating loss carryforwards, and a net deferred tax liability of $23.2 million.