Income Taxes	6 Months Ended
Jun. 30, 2018
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 adverse audit findings related to certain tax benefits and exemptions. 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. The Company’s effective income tax rate was 18.8% and 31.0% for the six months ended June 30, 2018 and 2017, respectively. The lower effective tax rate for the six months ended June 30, 2018, is primarily due to a reduction in the U.S. federal statutory tax rate from 35.0% to 21.0% as part of the TCJA and an increase in the excess tax benefit related to stock-based compensation. For the six months ended June 30, 2018, 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, partially offset by U.S. federal taxes on Global Intangible Low-Taxed Income (“GILTI”) enacted as part of the TCJA and an intercompany sale of intellectual property. For the six months ended June 30, 2017, 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 effects of accounting for stock-based compensation in accordance with the authoritative guidance for share-based payments and state income taxes. As of June 30, 2018, no changes have been made to the previously recorded provisional amounts related to the one-time transition tax and the re-measurement of the Company's deferred tax balances in its consolidated financial statements for the year ended December 31, 2017 due to the TCJA. Any changes to the provisional amounts will be recorded in the period in which the adjustments are made. These changes could arise from additional analysis, changes in assumptions or interpretations the Company has made, additional guidance that may be issued and actions the Company may take as a result of the TCJA. Beginning in 2018, the TCJA provides for a modified territorial tax system imposing an incremental tax on foreign income deemed to be taxed at a “low rate” (the aforementioned GILTI provisions). Under GAAP, an election must be made to either (1) treat taxes due related to GILTI as a current-period expense when incurred (the “period cost method”) or (2) factor such amounts into the measurement of deferred taxes (the “deferred method”). The Company is still evaluating the effects of these provisions and has not yet adopted a policy to account for the related impacts.

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 adverse audit findings related to certain tax benefits and exemptions. 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.

The Company’s effective income tax rate was 18.8% and 31.0% for the six months ended June 30, 2018 and 2017, respectively. The lower effective tax rate for the six months ended June 30, 2018, is primarily due to a reduction in the U.S. federal statutory tax rate from 35.0% to 21.0% as part of the TCJA and an increase in the excess tax benefit related to stock-based compensation.

For the six months ended June 30, 2018, 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, partially offset by U.S. federal taxes on Global Intangible Low-Taxed Income (“GILTI”) enacted as part of the TCJA and an intercompany sale of intellectual property.

For the six months ended June 30, 2017, 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 effects of accounting for stock-based compensation in accordance with the authoritative guidance for share-based payments and state income taxes.

As of June 30, 2018, no changes have been made to the previously recorded provisional amounts related to the one-time transition tax and the re-measurement of the Company's deferred tax balances in its consolidated financial statements for the year ended December 31, 2017 due to the TCJA. Any changes to the provisional amounts will be recorded in the period in which the adjustments are made. These changes could arise from additional analysis, changes in assumptions or interpretations the Company has made, additional guidance that may be issued and actions the Company may take as a result of the TCJA.

Beginning in 2018, the TCJA provides for a modified territorial tax system imposing an incremental tax on foreign income deemed to be taxed at a “low rate” (the aforementioned GILTI provisions). Under GAAP, an election must be made to either (1) treat taxes due related to GILTI as a current-period expense when incurred (the “period cost method”) or (2) factor such amounts into the measurement of deferred taxes (the “deferred method”). The Company is still evaluating the effects of these provisions and has not yet adopted a policy to account for the related impacts.