Acquisition - Schedule of Pro Forma and Reported Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Revenue	$ 120,558	$ 62,935	$ 61,511	$ 60,892	$ 62,780	$ 60,432	$ 77,476	$ 73,096	$ 305,896	$ 273,784	$ 255,098
Net income attributable to Onto Innovation Reported	$ (17,752)	$ 6,560	$ 5,526	$ 7,576	$ 8,082	$ 7,187	$ 14,697	$ 15,130	1,910	45,096	$ 32,909
Rudolph Technologies, Inc. [Member]
Business Acquisition [Line Items]
Revenue									66,261
Net revenue Pro Forma									525,455	598,307
Net income attributable to Onto Innovation Pro Forma									$ 901	$ 36,246