Schedule of Changes in Fair Value of Level 3 Contingent Consideration (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period		$ 15,581	$ 37,916	$ 45,102	$ 38,332
Acquisition of MiR		51,399		51,399
Foreign currency impact		(2,566)		(2,566)
Payments	[1]			(24,553)	(1,050)
Fair value adjustment	[2]	(3,500)	1,499	(8,468)	2,133
Balance at end of period		$ 60,914	$ 39,415	$ 60,914	$ 39,415

[1] In the six months ended July 1, 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 six months ended July 2, 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 six months ended July 1, 2018, the fair value of contingent consideration for the earn-out in connection with the acquisition of Universal Robots was decreased by $3.5 million and $8.5 million, respectively, primarily due to a decrease in forecasted revenue. In the three and six months ended July 2, 2017, the fair value of contingent consideration for the earn-out in connection with the acquisition of Universal Robots was increased by $1.5 million and $2.1 million, respectively, primarily due to a decrease in the discount rate.