Income Taxes	9 Months Ended
Sep. 29, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rates for the three and nine months ended September 29, 2018 were 21.5% and 20.1%, respectively, compared to effective tax rates for the three and nine months ended September 30, 2017 of 22.9% and 18.7%, respectively. The effective tax rate for the third quarter of 2018 was lower than the effective tax rate for the third quarter of 2017 primarily due to a third quarter 2017 accrual for taxes on certain undistributed earnings of non-US affiliates, offset in part by the impact of US tax reform and the acquisition of IXYS. The effective tax rate of the first nine months of 2018 is higher than the effective tax rates for the first nine months of 2017 primarily due to the impact of U.S. tax reform and the acquisition of IXYS. The effective tax rates for the 2017 periods were lower than the then applicable 35% U.S. statutory tax rate primarily due to income earned in lower tax jurisdictions. On December 22, 2017, the U.S. enacted legislation commonly referred to as the Tax Cuts and Jobs Act (the "Tax Act"). Among other things, the Tax Act reduces the U.S. corporate federal income tax rate from 35% to 21%, adds base broadening provisions which limit deductions and address excessive international tax planning, imposes a one-time tax (the “Toll Charge”) on accumulated earnings of certain non-U.S. subsidiaries and enables repatriation of earnings of non-U.S. subsidiaries free of U.S. federal income tax. Other than the Toll Charge (which, except for the IXYS impact, is applicable to the Company for 2017), the provisions will generally be applicable to the Company in 2018 and beyond. In accordance with the guidance provided in SEC Staff Accounting Bulletin (“SAB”) No. 118, in the fourth quarter of 2017 the Company recorded a charge of $47.0 million as a provisional reasonable estimate of the impact of the Tax Act, including $49.0 million for the Toll Charge net of $2.0 million for other net tax benefits. The Company did not adjust the provisional reasonable estimate in the first nine months of 2018. In addition, the Company recorded a preliminary estimate of $8.0 million for the Toll Charge associated with IXYS as part of the IXYS acquisition purchase price allocation (this estimate reflects a reduction of $2.0 million recorded in the third quarter of 2018). This estimate was reflected in the opening balance sheet as an increase to goodwill and other long-term liabilities. The Company is continuing to analyze the Tax Act and plans to finalize the 2017 provisional reasonable estimate within the measurement period outlined in SAB No. 118 and the IXYS Toll Charge estimate during the purchase price allocation period. The final charges may differ from the estimates if provisions of the Tax Act, and their interaction with other provisions of the U.S. Internal Revenue Code, are interpreted differently than interpretations made by the Company in determining the estimates, whether through issuance of administrative guidance, or through further review of the Tax Act by the Company and its advisors. Aside from these interpretation issues, the final charges may differ from the estimates due to refinements of accumulated non-U.S. earnings and tax pool data. The Company has elected to pay the 2017 Littelfuse Toll Charge and will elect to pay the 2018 IXYS Toll Charge over the eight-year period prescribed by the Tax Act. The long-term portion of these Toll Charges totaling $29.7 million (which includes the 2017 Littelfuse provisional reasonable estimate and the 2018 IXYS provisional estimate, partially offset by foreign tax credits, other current deductions and the actual 2018 and anticipated 2019 annual installment payments) is recorded in the Other long-term liabilities on the Condensed Consolidated Balance Sheet as of September 29, 2018. The Company recognized deferred tax liabilities of $12.0 million ($11.8 million for non-U.S. taxes and $0.2 million for U.S. state taxes) as of December 30, 2017 related to taxes on certain non-U.S. earnings which are not considered to be permanently reinvested. Some of these taxes may provide a U.S. federal income tax benefit as a foreign tax credit. However, due to uncertainty in regard to the Tax Act’s provisions, no such tax benefit was recorded as of December 30, 2017, and no such tax benefit was recorded in the first nine months of 2018. The Company will reconsider this provisional conclusion when it finalizes its 2017 preliminary reasonable estimate of the impact of the Tax Act, based upon interpretations and administrative guidance as of that time. One of the base broadening provisions of the Tax Act is commonly referred to as the “GILTI” provisions. In accordance with guidance issued by the FASB staff, the Company has not adopted an accounting policy for GILTI. Thus, deferred taxes were computed without consideration of the possible future impact of the GILTI provisions. The Company intends to adopt an accounting policy for GILTI within the measurement period outlined in SAB 118. Although such an accounting policy has not been adopted, the Company considered GILTI when determining the current portion of income tax expense recorded for the three and nine months ended September 29, 2018. Although certain administrative guidance has been issued, the appropriate application of many provisions of the Tax Act remain uncertain. The Company used its best judgement as to the application of these provisions in determining its income tax expense for the three and nine months ended September 29, 2018. Adjustments to income tax expense related to the first nine months of 2018 may be necessary if provisions of the Tax Act, and their interaction with other provisions of the U.S. Internal Revenue Code, are interpreted differently than interpretations made by the Company in determining its estimates, whether through issuance of administrative guidance, or through further review of the Tax Act by the Company and its advisors.

Income Taxes

The effective tax rates for the three and nine months ended September 29, 2018 were 21.5% and 20.1%, respectively, compared to effective tax rates for the three and nine months ended September 30, 2017 of 22.9% and 18.7%, respectively.

The effective tax rate for the third quarter of 2018 was lower than the effective tax rate for the third quarter of 2017 primarily due to a third quarter 2017 accrual for taxes on certain undistributed earnings of non-US affiliates, offset in part by the impact of US tax reform and the acquisition of IXYS. The effective tax rate of the first nine months of 2018 is higher than the effective tax rates for the first nine months of 2017 primarily due to the impact of U.S. tax reform and the acquisition of IXYS. The effective tax rates for the 2017 periods were lower than the then applicable 35% U.S. statutory tax rate primarily due to income earned in lower tax jurisdictions.

On December 22, 2017, the U.S. enacted legislation commonly referred to as the Tax Cuts and Jobs Act (the "Tax Act"). Among other things, the Tax Act reduces the U.S. corporate federal income tax rate from 35% to 21%, adds base broadening provisions which limit deductions and address excessive international tax planning, imposes a one-time tax (the “Toll Charge”) on accumulated earnings of certain non-U.S. subsidiaries and enables repatriation of earnings of non-U.S. subsidiaries free of U.S. federal income tax. Other than the Toll Charge (which, except for the IXYS impact, is applicable to the Company for 2017), the provisions will generally be applicable to the Company in 2018 and beyond.

In accordance with the guidance provided in SEC Staff Accounting Bulletin (“SAB”) No. 118, in the fourth quarter of 2017 the Company recorded a charge of $47.0 million as a provisional reasonable estimate of the impact of the Tax Act, including $49.0 million for the Toll Charge net of $2.0 million for other net tax benefits. The Company did not adjust the provisional reasonable estimate in the first nine months of 2018. In addition, the Company recorded a preliminary estimate of $8.0 million for the Toll Charge associated with IXYS as part of the IXYS acquisition purchase price allocation (this estimate reflects a reduction of $2.0 million recorded in the third quarter of 2018). This estimate was reflected in the opening balance sheet as an increase to goodwill and other long-term liabilities. The Company is continuing to analyze the Tax Act and plans to finalize the 2017 provisional reasonable estimate within the measurement period outlined in SAB No. 118 and the IXYS Toll Charge estimate during the purchase price allocation period. The final charges may differ from the estimates if provisions of the Tax Act, and their interaction with other provisions of the U.S. Internal Revenue Code, are interpreted differently than interpretations made by the Company in determining the estimates, whether through issuance of administrative guidance, or through further review of the Tax Act by the Company and its advisors. Aside from these interpretation issues, the final charges may differ from the estimates due to refinements of accumulated non-U.S. earnings and tax pool data.

The Company has elected to pay the 2017 Littelfuse Toll Charge and will elect to pay the 2018 IXYS Toll Charge over the eight-year period prescribed by the Tax Act. The long-term portion of these Toll Charges totaling $29.7 million (which includes the 2017 Littelfuse provisional reasonable estimate and the 2018 IXYS provisional estimate, partially offset by foreign tax credits, other current deductions and the actual 2018 and anticipated 2019 annual installment payments) is recorded in the Other long-term liabilities on the Condensed Consolidated Balance Sheet as of September 29, 2018.

The Company recognized deferred tax liabilities of $12.0 million ($11.8 million for non-U.S. taxes and $0.2 million for U.S. state taxes) as of December 30, 2017 related to taxes on certain non-U.S. earnings which are not considered to be permanently reinvested. Some of these taxes may provide a U.S. federal income tax benefit as a foreign tax credit. However, due to uncertainty in regard to the Tax Act’s provisions, no such tax benefit was recorded as of December 30, 2017, and no such tax benefit was recorded in the first nine months of 2018. The Company will reconsider this provisional conclusion when it finalizes its 2017 preliminary reasonable estimate of the impact of the Tax Act, based upon interpretations and administrative guidance as of that time.

One of the base broadening provisions of the Tax Act is commonly referred to as the “GILTI” provisions. In accordance with guidance issued by the FASB staff, the Company has not adopted an accounting policy for GILTI. Thus, deferred taxes were computed without consideration of the possible future impact of the GILTI provisions. The Company intends to adopt an accounting policy for GILTI within the measurement period outlined in SAB 118. Although such an accounting policy has not been adopted, the Company considered GILTI when determining the current portion of income tax expense recorded for the three and nine months ended September 29, 2018.

Although certain administrative guidance has been issued, the appropriate application of many provisions of the Tax Act remain uncertain. The Company used its best judgement as to the application of these provisions in determining its income tax expense for the three and nine months ended September 29, 2018. Adjustments to income tax expense related to the first nine months of 2018 may be necessary if provisions of the Tax Act, and their interaction with other provisions of the U.S. Internal Revenue Code, are interpreted differently than interpretations made by the Company in determining its estimates, whether through issuance of administrative guidance, or through further review of the Tax Act by the Company and its advisors.