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Schedule of Changes in Fair Value of Level 3 Contingent Consideration (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Oct. 04, 2015 | Sep. 28, 2014 | Oct. 04, 2015 | Sep. 28, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |
Balance at beginning of period |  | $ 35,595 | $ 2,230 | $ 3,350 | $ 2,230
Fair value adjustment | [1],[2] | (1,000) | (630) | (2,600) | (630)
Ending Balance |  | $ 34,595 | $ 1,600 | 34,595 | $ 1,600
Universal Robots |  |  |  |  |
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |
Acquisition |  |  |  | $ 33,845 |
[1] | In the nine months ended October 4, 2015, the fair value measurement of the contingent consideration for the earn-out in connection with the acquisition of ZTEC Instruments, Inc. was reduced by $1.6 million, to $0, because Teradyne and the Securityholder Representative, on behalf of the ZTEC securityholders, agreed to terminate the earn-out prior to the end of the December 31, 2015 earn-out period, with no payout in connection with the resolution of indemnity claims asserted by both Teradyne and the Securityholder Representative.
[2] | In the three and nine months ended October 4, 2015, the fair value of contingent consideration for the earn-out in connection with the acquisition of AIT was reduced by $1.0 million due to a decrease in the revenue probabilities in the periods of 2015 and 2016.

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