Net Income Per Share - Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 27, 2019	Sep. 27, 2019	Jun. 28, 2019	Mar. 29, 2019	Dec. 28, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 27, 2019	Dec. 28, 2018	Dec. 29, 2017
Numerator:
Net income (loss) attributable to UCT	$ (10,300)	$ 500	$ (200)	$ 600	$ (1,100)	$ (6,000)	$ 19,000	$ 24,700	$ (9,400)	$ 36,600	$ 75,100
Shares used in computation — basic:
Weighted average common shares outstanding									39.5	38.4	33.4
Shares used in computation — diluted:
Weighted average common shares outstanding									39.5	38.4	33.4
Dilutive effect of common shares outstanding subject to repurchase									0.0	0.5	0.9
Dilutive effect of options outstanding									0.0	0.0	0.0
Shares used in computing diluted net income (loss) per share									39.5	38.9	34.3
Net income (loss) per share attributable to UCT — basic									$ (0.24)	$ 0.95	$ 2.25
Net income (loss) per share attributable to UCT — diluted									$ (0.24)	$ 0.94	$ 2.19