Income Taxes	3 Months Ended
Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective income tax rate is based on estimated income for the year, the estimated composition of the income in different jurisdictions and discrete adjustments, if any, in the applicable quarterly periods. Potential discrete adjustments include tax charges or benefits related to stock-based compensation, changes in tax legislation, settlements of tax audits or assessments, uncertain tax positions and acquisitions, among other items. The Company is currently under audit in multiple jurisdictions and, in certain cases, is involved in litigation related to adverse audit determinations. In the second quarter of 2018, the Company filed an appeal with the Massachusetts Appellate Tax Board contesting the adverse audit findings related to certain tax benefits and exemptions. The Company has determined that it is more-likely-than-not that it will prevail, and no reserve has been recorded related to these controversies. Over the next 12 months, the Company’s current assumptions and positions could change based on audit determinations and other events impacting its analysis. Such events, if resolved unfavorably, could significantly impact the Company’s effective income tax rate and results of operations. The Company has estimated that an adverse ruling related to its Massachusetts controversy could result in an income tax charge of approximately $30.0 million. The Company’s effective income tax rate was 18.6% and 20.7% for the three months ended March 31, 2019 and 2018, respectively. The lower effective tax rate for the three months ended March 31, 2019, is primarily due to an increase in foreign income taxed at lower rates and a decrease to U.S. federal taxes on Global Intangible Low-Taxed Income ("GILTI"). These amounts were partially offset by an increase in the valuation allowance recorded against deferred tax assets related to state tax credits in which it is more likely than not that such credits will expire prior to utilization and an increase in non-deductible executive compensation. For the three months ended March 31, 2019, the effective income tax rate was lower than the federal statutory tax rate due to foreign income taxed at lower rates, the excess tax benefit related to stock-based compensation and the benefit of U.S. federal, state and foreign research and development credits. These amounts were partially offset by the valuation allowance recorded against deferred tax assets related to state tax credits, non-deductible executive compensation, state taxes and an intercompany sale of intellectual property. For the three months ended March 31, 2018, the effective income tax rate was lower than the federal statutory tax rate due to foreign income taxed at lower rates and the benefit of U.S. federal, state and foreign research and development credits, partially offset by the U.S. federal taxes on GILTI and an intercompany sale of intellectual property.

Income Taxes

The effective income tax rate is based on estimated income for the year, the estimated composition of the income in different jurisdictions and discrete adjustments, if any, in the applicable quarterly periods. Potential discrete adjustments include tax charges or benefits related to stock-based compensation, changes in tax legislation, settlements of tax audits or assessments, uncertain tax positions and acquisitions, among other items.

The Company is currently under audit in multiple jurisdictions and, in certain cases, is involved in litigation related to adverse audit determinations. In the second quarter of 2018, the Company filed an appeal with the Massachusetts Appellate Tax Board contesting the adverse audit findings related to certain tax benefits and exemptions. The Company has determined that it is more-likely-than-not that it will prevail, and no reserve has been recorded related to these controversies. Over the next 12 months, the Company’s current assumptions and positions could change based on audit determinations and other events impacting its analysis. Such events, if resolved unfavorably, could significantly impact the Company’s effective income tax rate and results of operations. The Company has estimated that an adverse ruling related to its Massachusetts controversy could result in an income tax charge of approximately $30.0 million.

The Company’s effective income tax rate was 18.6% and 20.7% for the three months ended March 31, 2019 and 2018, respectively. The lower effective tax rate for the three months ended March 31, 2019, is primarily due to an increase in foreign income taxed at lower rates and a decrease to U.S. federal taxes on Global Intangible Low-Taxed Income ("GILTI"). These amounts were partially offset by an increase in the valuation allowance recorded against deferred tax assets related to state tax credits in which it is more likely than not that such credits will expire prior to utilization and an increase in non-deductible executive compensation.

For the three months ended March 31, 2019, the effective income tax rate was lower than the federal statutory tax rate due to foreign income taxed at lower rates, the excess tax benefit related to stock-based compensation and the benefit of U.S. federal, state and foreign research and development credits. These amounts were partially offset by the valuation allowance recorded against deferred tax assets related to state tax credits, non-deductible executive compensation, state taxes and an intercompany sale of intellectual property.

For the three months ended March 31, 2018, the effective income tax rate was lower than the federal statutory tax rate due to foreign income taxed at lower rates and the benefit of U.S. federal, state and foreign research and development credits, partially offset by the U.S. federal taxes on GILTI and an intercompany sale of intellectual property.