Schedule of Changes in Fair Value of Level 3 Contingent Consideration (Parenthetical) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Apr. 04, 2021	Mar. 29, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Payments of contingent consideration			$ 8,852
Increase (decrease) in contingent consideration		$ (7,227)	(10,020)
Fair value of contingent consideration, Acquisition, Earnings.	[1],[2]	(7,227)	(10,020)
Maximum amount of contingent consideration paid for acquisition			8,852
Universal Robots (UR)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Payments of contingent consideration			8,900
Maximum amount of contingent consideration paid for acquisition			8,900
MiR
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Increase (decrease) in contingent consideration			2,900
Autoguide LLC [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Payments of contingent consideration		100,200
Increase (decrease) in contingent consideration			$ 7,100
Fair value of contingent consideration, Acquisition, Earnings.		7,200
Maximum amount of contingent consideration paid for acquisition		$ 100,200

[1] In the three months ended April 4, 2021, the fair value of contingent consideration for the earn-outs in connection with the acquisition of AutoGuide was reduced to zero, which resulted in a benefit of $7.2 million, primarily due to a decrease in forecasted revenues and earnings before interest and taxes. As of April 4, 2021, the maximum amount of contingent consideration that could be paid in connection with the acquisition of AutoGuide is $100.2 million. The remaining earn-out periods end on December 31, 2021 and December 31, 2022. The sellers of AutoGuide have filed an arbitration claim against Teradyne related to the earn-out alleging non-compliance with the earn-out provisions of the AutoGuide acquisition agreement. Teradyne disputes the allegations of non-compliance. The ultimate amount of contingent consideration for the earn-outs in connection with the acquisition of AutoGuide may be affected by the outcome of the dispute.

[2] In the three months ended March 29, 2020, the fair value of contingent consideration for the earn-outs in connection with the acquisitions of Mobile Industrial Robots Aps (“MiR”) and AutoGuide decreased by $2.9 million and $7.1 million, respectively, due to lower forecasts.