Net Income Per Share - Basic and Diluted Net Income (loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 26, 2020	Jun. 28, 2019	Jun. 26, 2020	Jun. 28, 2019
Numerator:
Net income (loss) attributable to UCT	$ 21.3	$ (0.2)	$ 30.7	$ 0.4
Shares used in computation — basic:
Weighted average common shares outstanding	40.1	39.4	39.9	39.3
Shares used in computation — diluted:
Weighted average common shares outstanding	40.1	39.4	39.9	39.3
Dilutive effect of common shares outstanding subject to repurchase	0.7		0.9	0.3
Shares used in computing diluted net income per share	40.8	39.4	40.8	39.6
Net income (loss) per share attributable to UCT — basic	$ 0.53	$ (0.01)	$ 0.77	$ 0.01
Net income (loss) per share attributable to UCT — diluted	$ 0.52	$ (0.01)	$ 0.75	$ 0.01