Income Taxes - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended			12 Months Ended
	Jan. 17, 2018	Dec. 29, 2018	Sep. 29, 2018	Dec. 30, 2017	Dec. 29, 2018	Jan. 17, 2018	Dec. 30, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
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		49,000
Toll charge, noncurrent		28,800
Foreign tax credits							13,000
Tax benefit for net operating losses								$ (3,000)
Income taxes paid					$ 46,200		31,800	35,600
Income tax refunds					4,300		13,700
Unremitted earnings of the Company’s non-U.S. subsidiaries		815,000			815,000
Deferred tax liabilities recognized on foreign earnings		12,700		12,000	$ 12,700		12,000
Income tax holiday per diluted share (in dollars per share)					$ 0.24
Interest expense					$ 1,500		900	900
Decrease due to a lapse in the statute of limitations					300
Interest accrued		5,900		3,300	5,900		3,300
Unrecognized tax benefits		18,259		7,660	18,259		7,660	$ 8,617
Unrecognized tax benefits that may be recognized in next fiscal year		3,500			3,500
China
Income Tax Contingency [Line Items]
Tax holidays					6,100
Foreign Tax Authority
Income Tax Contingency [Line Items]
Deferred tax liabilities recognized on foreign earnings		12,500		11,800	12,500		11,800
Domestic Tax Authority
Income Tax Contingency [Line Items]
Deferred tax liabilities recognized on foreign earnings		200		$ 200	$ 200		$ 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