Schedule of Changes in Fair Value of Level 3 Contingent Consideration (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2018	Oct. 01, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period		$ 60,914	$ 39,415	$ 45,102	$ 38,332
Acquisition of MiR				51,399
Foreign currency impact		796		(1,770)
Payments	[1]			(24,553)	(1,050)
Fair value adjustment	[2]	(768)	(286)	(9,236)	1,847
Balance at end of period		$ 60,942	$ 39,129	$ 60,942	$ 39,129

[1] In the nine months ended September 30, 2018, Teradyne paid $24.6 million of contingent consideration for the earn-out in connection with the acquisition of Universal Robots A/S ("Universal Robots"). In the nine months ended October 1, 2017, Teradyne paid $1.1 million of contingent consideration for the earn-out in connection with the acquisition of Avionics Interface Technology, LLC ("AIT").

[2] In the three and nine months ended September 30, 2018, the fair value of contingent consideration for the earn-out in connection with the acquisition of Universal Robots was decreased by $0.8 million and $9.2 million, respectively, primarily due to a decrease in forecasted revenue. In the nine months ended October 1, 2017, the fair value of contingent consideration for the earn-out in connection with the acquisition of Universal Robots was increased by $1.8 million due to an increase in forecasted revenue.