Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital	Treasury Shares [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total stock holder's Equity of UCT [Member]	Noncontrolling Interests [Member]
Beginning balance at Dec. 28, 2018	$ 451.0	$ 0.1	$ 290.4	$ (3.3)	$ 149.7	$ (0.6)	$ 436.3	$ 14.7
Beginning balance, Shares at Dec. 28, 2018		39.1		0.6
Issuance under employee stock plans	0.1		0.1				0.1
Issuance under employee stock plans, Shares		0.9
Stock-based compensation expense	9.1		9.1				9.1
Taxes paid related to net share settlement of equity awards	(1.7)		(1.7)				(1.7)
Taxes paid related to net share settlement of equity awards, Shares		(0.2)
Net income	2.0				0.9		0.9	1.1
Other comprehensive loss	(3.8)					(3.8)	(3.8)
Ending balance at Sep. 27, 2019	456.7	$ 0.1	297.9	$ (3.3)	150.6	(4.4)	440.9	15.8
Ending balance, Shares at Sep. 27, 2019		39.8		0.6
Beginning balance at Jun. 28, 2019	454.5	$ 0.1	294.9	$ (3.3)	150.1	(2.7)	439.1	15.4
Beginning balance, Shares at Jun. 28, 2019		39.5		0.6
Issuance under employee stock plans, Shares		0.3
Stock-based compensation expense	3.3		3.3				3.3
Taxes paid related to net share settlement of equity awards	(0.3)		(0.3)				(0.3)
Net income	0.9				0.5		0.5	0.4
Other comprehensive loss	(1.7)					(1.7)	(1.7)
Ending balance at Sep. 27, 2019	456.7	$ 0.1	297.9	$ (3.3)	150.6	(4.4)	440.9	15.8
Ending balance, Shares at Sep. 27, 2019		39.8		0.6
Beginning balance at Dec. 27, 2019	452.5	$ 0.1	300.9	$ (3.3)	140.3	(1.3)	436.7	15.8
Beginning balance, Shares at Dec. 27, 2019		39.9		0.6
Issuance under employee stock plans	0.2		0.2				0.2
Issuance under employee stock plans, Shares		0.7
Stock-based compensation expense	9.5		9.5				9.5
Taxes paid related to net share settlement of equity awards	(1.4)		(1.4)				(1.4)
Taxes paid related to net share settlement of equity awards, Shares		(0.1)
Net income	57.7				55.1		55.1	2.6
Ending balance at Sep. 25, 2020	518.5	$ 0.1	309.2	$ (3.3)	195.4	(1.3)	500.1	18.4
Ending balance, Shares at Sep. 25, 2020		40.5		0.6
Beginning balance at Jun. 26, 2020	488.2	$ 0.1	306.0	$ (3.3)	171.0	(3.3)	470.5	17.7
Beginning balance, Shares at Jun. 26, 2020		40.3		0.6
Issuance under employee stock plans, Shares		0.2
Stock-based compensation expense	3.2		3.2				3.2
Net income	25.1				24.4		24.4	0.7
Other comprehensive loss	2.0					2.0	2.0
Ending balance at Sep. 25, 2020	$ 518.5	$ 0.1	$ 309.2	$ (3.3)	$ 195.4	$ (1.3)	$ 500.1	$ 18.4
Ending balance, Shares at Sep. 25, 2020		40.5		0.6