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Retirement Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Defined Benefit Plan Disclosure
Fair value of pension plans assets totaled	$ 345,600,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
United States
Defined Benefit Plan Disclosure
Accumulated benefit obligation for defined benefit pension plans	357,000,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation / us-gaap_StatementGeographicalAxis = us-gaap_DomesticCountryMember	286,200,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation / us-gaap_StatementGeographicalAxis = us-gaap_DomesticCountryMember
Fair value of pension plans assets totaled	316,072,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_StatementGeographicalAxis = us-gaap_DomesticCountryMember	256,373,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_StatementGeographicalAxis = us-gaap_DomesticCountryMember
Foreign
Defined Benefit Plan Disclosure
Accumulated benefit obligation for defined benefit pension plans	49,800,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation / us-gaap_StatementGeographicalAxis = us-gaap_ForeignCountryMember	45,000,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation / us-gaap_StatementGeographicalAxis = us-gaap_ForeignCountryMember
Fair value of pension plans assets totaled	29,511,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_StatementGeographicalAxis = us-gaap_ForeignCountryMember	25,756,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_StatementGeographicalAxis = us-gaap_ForeignCountryMember
United States Plans
Defined Benefit Plan Disclosure
Percentage of expected return on plan assets assumption	5.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedStatesPlansMember
Discount rate utilized to determine future pension obligations	3.70%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedStatesPlansMember	4.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedStatesPlansMember
Fair value of pension plans assets totaled	316,100,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedStatesPlansMember
Contribution to defined benefit pension plans	30,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedStatesPlansMember
U.K. Defined Benefit Pension Plan
Defined Benefit Plan Disclosure
Fair value of pension plans assets totaled	28,500,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedKingdomDefinedBenefitPensionPlanMember
U.K. Defined Benefit Pension Plan | Fixed Income Funds
Defined Benefit Plan Disclosure
Target assets allocation percentage	80.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_FixedIncomeFundsMember / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedKingdomDefinedBenefitPensionPlanMember
U.K. Defined Benefit Pension Plan | Equity Securities
Defined Benefit Plan Disclosure
Target assets allocation percentage	20.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquitySecuritiesMember / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedKingdomDefinedBenefitPensionPlanMember
Other Foreign Defined Benefit Pension Plans
Defined Benefit Plan Disclosure
Fair value of pension plans assets totaled	1,000,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedContributionPlanTypeAxis = ter_OtherForeignMember
U.S. Supplemental Executive Defined Benefit Pension Plan
Defined Benefit Plan Disclosure
Contribution to defined benefit pension plans	1,800,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedStatesSupplementalExecutiveDefinedBenefitPensionPlanMember	1,700,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedContributionPlanTypeAxis = ter_UnitedStatesSupplementalExecutiveDefinedBenefitPensionPlanMember
Foreign Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Contribution to defined benefit pension plans	1,200,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedContributionPlanTypeAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember	2,500,000us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedContributionPlanTypeAxis = us-gaap_ForeignPensionPlansDefinedBenefitMember
Net Periodic Benefit Cost
Defined Benefit Plan Disclosure
Accumulated other comprehensive income (loss), prior service cost expected to be recognized	100,000us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = ter_NetPeriodicBenefitCostMember
Postretirement Benefit Costs | Scenario, Forecast
Defined Benefit Plan Disclosure
Accumulated other comprehensive income (loss), prior service cost expected to be recognized			$ (600,000)us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PostretirementBenefitCostsMember / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember

X

- Definition

For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Accumulated Benefit Obligation

-URI http://asc.fasb.org/extlink&oid=6503844



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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X

- Definition

The interest rate used to adjust for the time value of money for the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(1)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Long-Term Rate of Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512013



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

The increase in the fair value of plan assets from contributions made by the employer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

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- Definition

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

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-Section 35

-Paragraph 50

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- Definition

Amount included in accumulated other comprehensive income (AOCI) related to prior service cost (credit) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

+ References

No definition available.

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Target allocation of investments of this type to total plan assets presented on a weighted average basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

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