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Debt instrument base rate percentage.

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Number of holders excerised the conversion option.

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Payments for Convertible Note Hedge, Net, Financing Activities

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The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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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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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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

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Amount, after accumulated amortization, of debt discount.

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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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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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Debt - Additional Information (Detail)				12 Months Ended
Debt - Additional Information (Detail)	Feb. 22, 2021 USD ($) Holders	May 01, 2020 USD ($)	Dec. 12, 2016 USD ($) Customer shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2016 USD ($)	Apr. 27, 2015 USD ($)
Debt Instrument
Repurchase of common stock				$ 88,465,000	$ 500,000,000	$ 823,478,000
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 rate 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.
Term of revolving credit facility				3 years
Convertible common shares				$ 3,787,000
Convertible Common Shares [Member]
Debt Instrument
Convertible common shares				37,000,000
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	459,971,000	$ 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			2,000,000.0
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				$ 31.56
Shares that would be issued upon conversion \| shares				14,600,000
Strike price per share of warrant \| $ / shares				$ 39.60
Debt instrument, convertible, carrying amount of equity component				$ 100,800,000
Debt instrument, effective annual interest rate				5.00%
Financing cost				$ 3,300,000			$ 7,200,000
Debt issuance costs, amortization period				7 years
Unamortized discount				$ 49,900,000
Debt Instrument, convertible, remaining discount amortization period				3 years
Value of notes converted				$ 1,747,500,000
1.25% Convertible Senior Unsecured Notes Due December 15, 2023 \| Subsequent Event
Debt Instrument
Number of holders excerised the conversion option \| Holders	24
Debt instrument conversion converted instrument amount	$ 51,000,000.0
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			$ 1,000,000
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
Term of loan, years				5 years
Credit facility, borrowing capacity								$ 350,000,000
Revolving Credit Facility \| Maximum \| Truist Bank [Member]
Debt Instrument
Commitment fee percentage of unused portion of credit facility				0.40%
Revolving Credit Facility \| Minimum \| Truist Bank [Member]
Debt Instrument
Commitment fee percentage of unused portion of credit facility				0.25%
Revolving Credit Facility \| Base Rate \| Maximum \| Truist Bank [Member]
Debt Instrument
Debt instrument, basis spread on variable rate				1.25%
Revolving Credit Facility \| Base Rate \| Minimum \| Truist Bank [Member]
Debt Instrument
Debt instrument, basis spread on variable rate				0.50%
Revolving Credit Facility \| London Interbank Offered Rate (LIBOR) \| Truist Bank [Member]
Debt Instrument
Debt Instrument Base Rate Percentage				0.75%
Revolving Credit Facility \| London Interbank Offered Rate (LIBOR) \| Maximum \| Truist Bank [Member]
Debt Instrument
Debt instrument, basis spread on variable rate				2.25%
Revolving Credit Facility \| London Interbank Offered Rate (LIBOR) \| Minimum \| Truist Bank [Member]
Debt Instrument
Debt instrument, basis spread on variable rate				1.50%