Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 28, 2018	Sep. 29, 2017
Income Statement [Abstract]
Sales	$ 234,079	$ 242,610	$ 839,134	$ 675,465
Cost of goods sold	199,084	199,914	709,270	551,903
Gross profit	34,995	42,696	129,864	123,562
Operating expenses:
Research and development	3,284	2,722	9,228	8,402
Sales and marketing	3,839	3,662	11,274	10,064
General and administrative	26,950	13,050	58,868	37,656
Total operating expenses	34,073	19,434	79,370	56,122
Income from operations	922	23,262	50,494	67,440
Interest and other income (expense), net	(2,766)	(19)	(3,249)	(2,077)
Income (loss) before provision for income taxes	(1,844)	23,243	47,245	65,363
Income tax provision	4,596	3,527	9,984	11,127
Net income (loss)	(6,440)	19,716	37,261	54,236
Net loss attributable to noncontrolling interest	(443)		(443)
Net income (loss) attributable to Ultra Clean Holdings, Inc.	$ (5,997)	$ 19,716	$ 37,704	$ 54,236
Net income (loss) per share attributable to Ultra Clean Holdings, Inc. common stockholders:
Basic	$ (0.15)	$ 0.59	$ 0.99	$ 1.63
Diluted	$ (0.15)	$ 0.57	$ 0.97	$ 1.59
Shares used in computing net income (loss) per share:
Basic	38,930	33,540	38,152	33,342
Diluted	38,930	34,360	38,745	34,216