Defined benefit plan assumptions used calculating benefit obligation initial medical trend.

No definition available.

Name:	ter_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationInitialMedicalTrend
Namespace Prefix:	ter_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined benefit plan assumptions used calculating benefit obligation medical cost trend rate decrease to ultimate rate in year.

+ References

No definition available.

+ Details

Name:	ter_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationMedicalCostTrendRateDecreaseToUltimateRateInYear
Namespace Prefix:	ter_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined benefit plan assumptions used calculating benefit obligation salary progression rate.

+ References

No definition available.

+ Details

Name:	ter_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationSalaryProgressionRate
Namespace Prefix:	ter_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (l)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=us-gaap_ForeignPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Schedule of Weighted Average Assumptions to Determine Pension Obligations (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018	Jan. 01, 2017
Postretirement Benefit Plans
Defined Benefit Plan Disclosure
Discount rate	3.00%	4.00%	3.40%
Initial medical trend	7.10%	7.50%	7.90%
Ultimate health care trend	4.50%	4.50%	4.50%	4.50%	4.50%	5.00%
Medical cost trend rate decrease to ultimate rate in year	2026	2026	2026
UNITED STATES
Defined Benefit Plan Disclosure
Discount rate	3.00%	4.10%
Salary progression rate	2.60%	2.50%
Foreign Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure
Discount rate	1.10%	1.80%
Salary progression rate	2.50%	2.60%