Income Taxes - Valuation allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Changes in the valuation allowance for deferred tax assets
Undistributed earnings of foreign subsidiaries	$ 71,500
Provision for foreign withholding tax and state income taxes	0
Valuation Allowance for Deferred Tax Assets
Changes in the valuation allowance for deferred tax assets
Balance at Beginning of Period	4,975	$ 6,518	$ 12,361
Additions Charged to Expenses	1,044	435	2,110
Additions Charged to Other Accounts			1,732
Deductions	(1,533)	(1,978)	(9,685)
Balance at End of Period	$ 4,486	$ 4,975	$ 6,518