Summary of Significant Accounting Policies and Other Information - Narrative (Details) $ in Thousands, € in Millions		3 Months Ended							12 Months Ended
	Jan. 17, 2018 USD ($)	Sep. 26, 2020 USD ($)	Jun. 27, 2020 USD ($)	Dec. 28, 2019 USD ($)	Jun. 29, 2019 USD ($)	Mar. 30, 2019 USD ($)	Dec. 29, 2018 USD ($)	Sep. 29, 2018 USD ($)	Dec. 26, 2020 USD ($) reporting_unit	Dec. 28, 2019 USD ($)	Dec. 29, 2018 USD ($)	Dec. 26, 2020 EUR (€)	Sep. 27, 2020	Dec. 28, 2019 EUR (€)
Summary of Significant Accounting Policies and Other Information
Cost of sales									$ 944,523	$ 957,578	$ 1,065,053
Selling, general, and administrative expenses									204,507	220,448	276,329
Research and development expenses									52,538	79,997	87,264
Equity investment				$ 12,969					19,186	12,969
Gain (loss) from equity method investments									0		(600)
Equity method investments				11,100					11,400	11,100
Impairment charges		$ 100		4,200	$ 200	$ 2,800			36,078	322	2,218
Goodwill impairment			$ 33,800						33,841
Goodwill				820,589			$ 826,715		$ 816,812	820,589	826,715
Number of reporting units | reporting_unit									7
Trade receivables, allowances				1,300					$ 1,400	1,300
Foreign exchange (gain) loss									(14,875)	5,224	(863)
Loss contingency accrual				1,100					2,900	1,100		€ 2.3		€ 1.0
TCJA one-time charge							3,200
Toll charge, noncurrent									(20,800)
Toll charge, current									3,000
90 days past due
Summary of Significant Accounting Policies and Other Information
Trade receivables, allowances				1,000					1,000	1,000
Other Expense
Summary of Significant Accounting Policies and Other Information
Impairment charges									100	7,300
Selling, General and Administrative Expenses
Summary of Significant Accounting Policies and Other Information
Advertising expense									2,100	2,700	2,800
Shipping and handling cost and expenses | Selling, General and Administrative Expenses
Summary of Significant Accounting Policies and Other Information
Cost of sales									$ 11,100	11,000	12,300
Land use rights
Summary of Significant Accounting Policies and Other Information
Finite lived intangible asset weighted average useful life (years)									50 years
Electronics Non Silicon Unit
Summary of Significant Accounting Policies and Other Information
Percentage of fair value in excess of carrying value													218.00%
Electronics (Silicon) Unit
Summary of Significant Accounting Policies and Other Information
Percentage of fair value in excess of carrying value													44.00%
Passenger Car
Summary of Significant Accounting Policies and Other Information
Percentage of fair value in excess of carrying value													160.00%
Commercial Vehicle Products
Summary of Significant Accounting Policies and Other Information
Percentage of fair value in excess of carrying value													137.00%
Automotive Sensors
Summary of Significant Accounting Policies and Other Information
Goodwill impairment			$ 33,800
Goodwill									$ 9,800
Sensors
Summary of Significant Accounting Policies and Other Information
Percentage of fair value in excess of carrying value													59.00%
Relay Unit
Summary of Significant Accounting Policies and Other Information
Percentage of fair value in excess of carrying value													139.00%
Fuse Unit
Summary of Significant Accounting Policies and Other Information
Percentage of fair value in excess of carrying value													210.00%
Minimum | Trademarks and tradenames
Summary of Significant Accounting Policies and Other Information
Finite lived intangible asset weighted average useful life (years)									5 years
Minimum | Patents, licenses and software
Summary of Significant Accounting Policies and Other Information
Finite lived intangible asset weighted average useful life (years)									5 years
Minimum | Distribution network
Summary of Significant Accounting Policies and Other Information
Finite lived intangible asset weighted average useful life (years)									4 years
Maximum | Trademarks and tradenames
Summary of Significant Accounting Policies and Other Information
Finite lived intangible asset weighted average useful life (years)									20 years
Maximum | Patents, licenses and software
Summary of Significant Accounting Policies and Other Information
Finite lived intangible asset weighted average useful life (years)									17 years
Maximum | Distribution network
Summary of Significant Accounting Policies and Other Information
Finite lived intangible asset weighted average useful life (years)									10 years
Building
Summary of Significant Accounting Policies and Other Information
Useful life (in years)									21 years
Equipment | Minimum
Summary of Significant Accounting Policies and Other Information
Useful life (in years)									3 years
Equipment | Maximum
Summary of Significant Accounting Policies and Other Information
Useful life (in years)									10 years
Furniture and Fixtures
Summary of Significant Accounting Policies and Other Information
Useful life (in years)									7 years
Tools, Dies and Molds
Summary of Significant Accounting Policies and Other Information
Useful life (in years)									5 years
Computer Equipment
Summary of Significant Accounting Policies and Other Information
Useful life (in years)									3 years
Other Noncurrent Assets
Summary of Significant Accounting Policies and Other Information
Marketable securities				10,500					$ 13,200	10,500
Other Assets
Summary of Significant Accounting Policies and Other Information
Equity investment				$ 400					$ 500	$ 400
Polytronics
Summary of Significant Accounting Policies and Other Information
Ownership percentage				7.20%					7.20%	7.20%		7.20%		7.20%
Equity investment				$ 12,800					$ 19,200	$ 12,800		€ 15.7		€ 11.6
Powersem | Equity Method
Summary of Significant Accounting Policies and Other Information
Ownership percentage									45.00%			45.00%
EB Tech | Equity Method
Summary of Significant Accounting Policies and Other Information
Ownership percentage									19.00%			19.00%
ATEC | Equity Method
Summary of Significant Accounting Policies and Other Information
Ownership percentage									24.00%			24.00%
Toll Charge
Summary of Significant Accounting Policies and Other Information
TCJA one-time charge							2,300
Other Items
Summary of Significant Accounting Policies and Other Information
TCJA one-time charge							900
IXYS Corporation
Summary of Significant Accounting Policies and Other Information
Goodwill	$ 382,360
IXYS Corporation | Toll Charge
Summary of Significant Accounting Policies and Other Information
TCJA one-time charge	$ 7,000						$ 7,000	$ (2,000)
Revision of Prior Period
Summary of Significant Accounting Policies and Other Information
Cost of sales										(4,800)	(900)
Selling, general, and administrative expenses										(7,600)	$ (11,700)
Research and development expenses										$ (500)