Selected Quarterly Financial Data - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Acquisition related costs	$ 1,900	$ 3,200	$ 1,500	$ 2,400	$ 3,200	$ 2,900	$ 2,400	$ 11,700
Restructuring, impairment and other costs	2,100	$ 2,500	5,700						$ 13,033	$ 12,583
Impairment charges	4,200		200	2,800					322	2,218	$ 0
Benefit for previously unrecognized tax benefits in respect of which the statute of limitation has expired	$ 3,300				1,500				2,758	1,257
Loss on sale of building			$ 400
Loss on disposal of a business				2,600
Restructuring costs				2,700	2,400	5,200	4,200	800
Gain related to acquisition of Monolith				$ 300
TCJA one-time charge					3,200
Backlog amortization costs								2,500
Purchase accounting inventory adjustments								17,900
Stock compensation expense									19,046	27,431	16,315
Selling, General and Administrative Expenses
Acquisition related costs									2,700
IXYS Corporation
Acquisition related costs									2,200	11,000
Backlog amortization costs					$ 3,700	$ 3,100	3,100
Purchase accounting inventory adjustments							$ 19,000
IXYS Corporation | Selling, General and Administrative Expenses
Stock compensation expense								$ 4,500
Other Segments | Selling, General and Administrative Expenses
Acquisition related costs											$ 8,000
Other Segments | Operating Income (Loss)
Acquisition related costs									$ 8,900	88,700
Impairment charges										5,800
Backlog amortization costs										12,400
Change in control expense										$ 2,100