Net Loss Per Share - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 27, 2025	Jun. 28, 2024	Jun. 27, 2025	Jun. 28, 2024
Numerator:
Net income (loss) attributable to UCT	$ (162.0)	$ 19.1	$ (167.0)	$ 9.7
Shares used in computation — basic:
Weighted average common shares outstanding (in shares)	45.2	44.9	45.2	44.7
Shares used in computation — diluted:
Weighted average common shares outstanding (in shares)	45.2	44.9	45.2	44.7
Effect of potential dilutive securities:
Employee stock plans (in shares)	0.0	0.5	0.0	0.6
Diluted weighted average common shares outstanding (in shares)	45.2	45.4	45.2	45.3
Net income (loss) per share attributable to UCT:
Basic (in dollars per share)	$ (3.58)	$ 0.43	$ (3.70)	$ 0.22
Diluted (in dollars per share)	$ (3.58)	$ 0.42	$ (3.70)	$ 0.21