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Debt - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended		12 Months Ended	0 Months Ended		3 Months Ended
	Mar. 31, 2009	Mar. 30, 2014	Sep. 30, 2013	Dec. 31, 2014	Mar. 13, 2014	Apr. 01, 2009	Apr. 05, 2015
Debt Instrument
Borrowings from local bank	$ 10,000,000us-gaap_LoansPayableToBank
Term of loan, years	5 years
Debt instrument, interest rate, stated percentage	0.80%us-gaap_DebtInstrumentInterestRateStatedPercentage
Loan collateralized by real estate mortgage	6,000,000us-gaap_MortgageLoansOnRealEstate
Unsecured loan	4,000,000us-gaap_UnsecuredDebt
Semiannual principal payments of loan		1,000,000us-gaap_DebtInstrumentPeriodicPaymentPrincipal	1,000,000us-gaap_DebtInstrumentPeriodicPaymentPrincipal
Payments of long-term debt		190,975,000us-gaap_RepaymentsOfLongTermDebt
Common stock shares were issued for warrants exercised				21,200,000ter_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrants
Strike price per share of warrant				$ 7.6348ter_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRightsIssued
4.50% Convertible Senior Notes Due March 15, 2014
Debt Instrument
Debt instrument, interest rate, stated percentage	4.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember
Aggregate principal amount	175,000,000us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember					190,000,000us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember
Additional aggregate principal amount	1,000ter_AdditionalAggregatePrincipalAmount / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember					15,000,000ter_AdditionalAggregatePrincipalAmount / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember
Senior notes maturity date	Mar. 15, 2014					Mar. 15, 2014
Conversion rate in number of shares	182.65ter_CommonSharesAttributableToConversionOfDebtInstrument / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember			131.95ter_CommonSharesAttributableToConversionOfDebtInstrument / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember
Number of shares excluded for conversion rate calculation				50.7ter_CommonStockSharesExcludingSubjectToConversion / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember
Trading days used to determine average price per share				25 days
Average trading price of common shares				$ 19.74us-gaap_DebtInstrumentConvertibleStockPriceTrigger / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember
Payments of long-term debt							$ 190,000,000us-gaap_RepaymentsOfLongTermDebt / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember
Stock issued in conversion of notes							25,100,000us-gaap_DebtConversionConvertedInstrumentSharesIssued1 / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember
Stock received and retired					25,100,000us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_DebtInstrumentAxis = ter_FourPointFiveZeroPercentConvertibleSeniorNotesDueMarchFifteenTwoThousandFourteenMember

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Additional aggregate principal amount.

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Common Shares Attributable To Conversion Of Debt Instrument

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Common Stock Shares Excluding Subject To Conversion

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The number of shares issued in exchange for the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or payments in the period.

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Price of the entity's common stock which would be required to be attained for the conversion feature embedded in the debt instrument to become effective.

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

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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 of the required periodic payments applied to principal.

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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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Including the current and noncurrent portions, carrying value as of the balance sheet date of loans from a bank with maturities initially due after one year or beyond the normal operating cycle if longer.

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Total carrying amount of mortgage loans as of the balance sheet date.

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The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

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