Antidilution adjustments of convertible note hedges.

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Class of warrant or right exercise price of warrants or rights issued.

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Debt instrument, convertible, maximum threshold percentage.

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Debt instrument issuance costs amortization period.

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Payments for Convertible Note Hedge, Net, Financing Activities

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Expiration, mandatory redemption, or due date, in CCYY-MM-DD format, of the financial instrument issued in exchange for the original debt being converted in a noncash or part noncash transaction.

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Amount of a favorable spread to a debt holder between the amount of debt being converted and the value of the securities received upon conversion. This is an embedded conversion feature of convertible debt issued that is in-the-money at the commitment date.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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The price per share of the conversion feature embedded in the debt instrument.

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Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

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Face (par) amount of debt instrument at time of issuance.

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Description of the frequency of periodic payments (monthly, quarterly, annual).

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount, after accumulated amortization, of debt discount.

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Amount, before accumulated amortization, of debt issuance costs related to line of credit arrangements. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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The maximum amount of borrowing capacity under a line of credit that is available as of the balance sheet date for a specific purpose other than for financing goods acquired for inventory or imminent delivery to a customer.

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No definition available.

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Description of the interest rate for the amounts borrowed under the credit facility, including the terms and the method for determining the interest rate (for example, fixed or variable, LIBOR plus a percentage, increasing rate, timing of interest rate resets, remarketing provisions).

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Period between issuance and maturity of long-term debt, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The cash outflow to reacquire common stock during the period.

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The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Debt - Additional Information (Detail) $ / shares in Units, shares in Millions			9 Months Ended
	May 01, 2020 USD ($)	Dec. 12, 2016 USD ($) Customer shares	Sep. 27, 2020 USD ($) $ / shares shares	Sep. 29, 2019 USD ($) shares	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument
Repurchase of common stock			$ 88,465,000	$ 368,782,000
Repurchase of stock, shares \| shares			1.5	8.8
Term of loan, years	3 years
Line of Credit Facility, Maximum Borrowing Capacity	$ 400,000,000.0
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases	$ 150,000,000.0
Line of Credit Facility, Interest Rate Description	The interest rates applicable to loans under the Credit Facility are, at Teradyne’s option, equal to either a base rate plus a margin ranging from 0.50% to 1.25% per annum or LIBOR, a minimum of 0.75%, plus a margin ranging from 1.50% to 2.25% per annum, based on the consolidated leverage ratio of Teradyne. In addition, Teradyne will pay a commitment fee on the unused portion of the commitments under the Credit Facility ranging from 0.25% to 0.40% per annum, based on the then applicable consolidated leverage ratio.
Collateral Pledged [Member]
Debt Instrument
Line of Credit Facility, Interest Rate Description	65
1.25% Convertible Senior Unsecured Notes Due December 15, 2023
Debt Instrument
Aggregate principal amount		$ 460,000,000.0	$ 459,973,000			$ 460,000,000
Debt instrument, interest rate, stated percentage		1.25%
Debt instrument, net proceeds after issuance costs		$ 450,800,000
Payment for net cost of convertible note hedges net of warrant proceeds		33,000,000.0	$ 33,000,000.0
Repurchase of common stock		$ 50,100,000
Repurchase of stock, shares \| shares		2.0
Senior notes maturity date		Dec. 15, 2023
Debt instrument, frequency of periodic payment		payable semiannually in arrears on June 15 and December 15 of each year
Debt instrument, conversion option expiration date		Sep. 15, 2023
Debt instrument conversion price \| $ / shares			$ 31.57
Shares that would be issued upon conversion \| shares			14.6
Strike price per share of warrant \| $ / shares			$ 39.62
Debt instrument, convertible, carrying amount of equity component			$ 100,800,000
Debt instrument, effective annual interest rate			5.00%
Financing cost			$ 7,200,000		$ 3,600,000
Debt issuance costs, amortization period			7 years
Unamortized discount			$ 53,800,000
Debt Instrument, convertible, remaining discount amortization period			3 years 3 months 18 days
Value of notes converted			$ 1,132,400,000
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 \| Conversion option one
Debt Instrument
Trading days measurement period \| Customer		20
Consecutive trading days measurement period \| Customer		30
Percentage of conversion price		130.00%
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 \| Conversion option two
Debt Instrument
Aggregate principal amount		$ 1,000
Trading days measurement period \| Customer		5
Consecutive trading days measurement period \| Customer		5
Percentage of closing sale price of common stock and conversion rate product		98.00%
Revolving Credit Facility
Debt Instrument
Revolving credit facility costs incurred			$ 3,500,000
Term of revolving credit facility			3 years