Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Shares [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total stockholders' Equity of UCT [Member]	Noncontrolling Interests [Member]
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		39,900,000		600,000
Issuance under employee stock plans	0.2		0.2				0.2
Issuance under employee stock plans, Shares		700,000
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		100,000
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		40,500,000		600,000
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		(100,000)
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		40,300,000		600,000
Issuance under employee stock plans, Shares		200,000
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		40,500,000		600,000
Beginning balance at Dec. 25, 2020	551.2	$ 0.1	312.8	$ (3.3)	217.9	5.1	532.6	18.6
Beginning balance, Shares at Dec. 25, 2020		40,600,000		600,000
Issuance of common stock in public offering	192.8		192.8				192.8
Issuance of common stock in public offering, Shares		3,700,000
Issuance under employee stock plans	0.3		0.3				0.3
Issuance under employee stock plans, Shares		700,000
Employees’ taxes paid upon vesting of restricted stock units	(7.0)		(7.0)				(7.0)
Employees' taxes paid upon vesting of restricted stock units, Shares		(100,000)
Stock-based compensation expense	11.5		11.5				11.5
Noncontrolling interests from acquisition of Ham-Let	1.8							1.8
Net income	77.6				74.0		74.0	3.6
Dividend payments to a joint venture shareholder	(0.1)							(0.1)
Reclassification of common stock purchase obligation liability upon modification of agreement (see Note 11)	16.4							16.4
Other comprehensive loss	(4.2)					(4.2)	(4.2)
Ending balance at Sep. 24, 2021	840.3	$ 0.1	510.4	$ (3.3)	291.9	0.9	800.0	40.3
Ending balance, Shares at Sep. 24, 2021		44,900,000		600,000
Beginning balance at Jun. 25, 2021	788.7	$ 0.1	506.1	$ (3.3)	260.0	4.6	767.5	21.2
Beginning balance, Shares at Jun. 25, 2021		44,800,000		600,000
Issuance under employee stock plans, Shares		100,000
Stock-based compensation expense	4.3		4.3				4.3
Noncontrolling interests from acquisition of Ham-Let	0.6							0.6
Net income	34.0				31.9		31.9	2.1
Reclassification of common stock purchase obligation liability upon modification of agreement (see Note 11)	16.4							16.4
Other comprehensive loss	(3.7)					(3.7)	(3.7)
Ending balance at Sep. 24, 2021	$ 840.3	$ 0.1	$ 510.4	$ (3.3)	$ 291.9	$ 0.9	$ 800.0	$ 40.3
Ending balance, Shares at Sep. 24, 2021		44,900,000		600,000