Income Taxes - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended				12 Months Ended
	Jan. 17, 2018	Dec. 28, 2019	Dec. 29, 2018	Sep. 29, 2018	Dec. 30, 2017	Dec. 28, 2019	Dec. 29, 2018	Jan. 17, 2018	Dec. 30, 2017
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Period Increase (Decrease)						$ 3,300
Provisional estimate of Tax Act					$ 47,000
Preliminary estimate of toll charge					49,000				$ 49,000
Other net tax benefits					(2,000)
TCJA one-time charge			$ 3,200
Toll charge, noncurrent						23,800
Toll charge, current						3,000
Benefit for previously unrecognized tax benefits in respect of which the statute of limitation has expired		$ 3,300	1,500			2,758	$ 1,257
Foreign tax credits									13,000
Income taxes paid						47,600	46,200		31,800
Income tax refunds						7,100	4,300		13,700
Unremitted earnings of the Company’s non-U.S. subsidiaries		776,000				776,000
Deferred tax liabilities recognized on foreign earnings		13,000	12,700			$ 13,000	12,700
Income tax holiday per diluted share (in dollars per share)						$ 0.17
Interest expense						$ 1,300	1,500		900
Decrease due to a lapse in the statute of limitations						600	300
Interest accrued		7,200	5,900			7,200	5,900
Unrecognized tax benefits		16,721	18,259		$ 7,660	16,721	18,259		$ 7,660
Unrecognized tax benefits that may be recognized in next fiscal year		100				100
China
Income Tax Contingency [Line Items]
Tax holidays						4,200
Foreign Tax Authority
Income Tax Contingency [Line Items]
Deferred tax liabilities recognized on foreign earnings		12,600	12,500			12,600	12,500
Domestic Tax Authority
Income Tax Contingency [Line Items]
Deferred tax liabilities recognized on foreign earnings		$ 400	200			$ 400	$ 200
Toll Charge
Income Tax Contingency [Line Items]
TCJA one-time charge			2,300
Toll Charge | IXYS Corporation
Income Tax Contingency [Line Items]
TCJA one-time charge	$ 7,000		(1,000)	$ (2,000)				$ 7,000
Other Items
Income Tax Contingency [Line Items]
TCJA one-time charge			$ 900