Schedule of Changes in Fair Value of Level 3 Contingent Consideration (Detail) - USD ($) $ in Thousands		3 Months Ended
		Apr. 01, 2018	Apr. 02, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period		$ 45,102	$ 38,332
Payments	[1]	(24,553)	(1,050)
Fair value adjustment	[2]	(4,968)	634
Balance at end of period		$ 15,581	$ 37,916

[1] In the three months ended April 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 three months ended April 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 months ended April 1, 2018, the fair value of contingent consideration for the earn-out in connection with the acquisition of Universal Robots was decreased by $5.0 million, primarily due to a decrease in forecasted revenue. In the three months ended April 2, 2017, the fair value of contingent consideration for the earn-out in connection with the acquisition of Universal Robots was increased by $0.6 million primarily due to an increase in forecasted revenue and a decrease in the discount rate.