Schedule of Changes in Fair Value of Level 3 Contingent Consideration (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Oct. 03, 2021	Sep. 27, 2020	Oct. 03, 2021	Sep. 27, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period		$ 0	$ 49,737	$ 7,227	$ 39,705
Fair value adjustment	[1],[2],[3]	0	(27,206)	(7,227)	(7,967)
Foreign currency impact		0	0	0	(355)
Payments	[4]				(8,852)
Balance at end of period		$ 0	$ 22,531	$ 0	$ 22,531

[1] In the nine months ended October 3, 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 October 3, 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 allegations of non-compliance with its earn-out obligations. 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 arbitration (see Note R: “Commitments and Contingencies”).

[2] In the nine months ended September 27, 2020, the fair value of contingent consideration for the earn-outs in connection with the acquisition of Mobile Industrial Robots (“MiR”) decreased by $3.5 million due to lower forecasted results.

[3] In the three and nine months ended September 27, 2020, the fair value of contingent consideration for the earn-outs in connection with the acquisition of AutoGuide decreased by $27.2 million and $4.4 million, respectively, due to lower forecasted revenues and earnings before interest and taxes.

[4] In the nine months ended September 27, 2020, Teradyne paid $8.9 million of contingent consideration for the earn-out in connection with the acquisition of MiR.