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Computation of Basic and Diluted Net Income Per Common Share (Parenthetical) (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Convertible Notes
Net Income Loss Per Common Share
Initial debt conversion price	$ 5.48us-gaap_DebtInstrumentConvertibleConversionPrice1 / us-gaap_DebtInstrumentAxis = ter_ConvertibleNoteMember
Shares that would be issued upon conversion	34.7ter_AntidilutionAdjustmentsOfConvertibleNoteHedges / us-gaap_DebtInstrumentAxis = ter_ConvertibleNoteMember
Convertible Notes Hedge Warrant
Net Income Loss Per Common Share
Initial debt conversion price	$ 7.67us-gaap_DebtInstrumentConvertibleConversionPrice1 / us-gaap_DebtInstrumentAxis = ter_ConvertibleNotesHedgeAndWarrantMember
Shares that would be issued upon conversion	34.7ter_AntidilutionAdjustmentsOfConvertibleNoteHedges / us-gaap_DebtInstrumentAxis = ter_ConvertibleNotesHedgeAndWarrantMember

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- Definition

Antidilution adjustments of convertible note hedges.

+ References

No definition available.

+ Details

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- Details

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- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6928298&loc=SL6031898-161870

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