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Computation of Basic and Diluted Net (Loss) Income Per Common Share (Parenthetical) (Detail) shares in Millions	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Convertible Notes
Net Income Loss Per Common Share
Initial debt conversion price | $ / shares	$ 31.70
Shares that would be issued upon conversion | shares	14.5
Convertible Notes Hedge Warrant
Net Income Loss Per Common Share
Initial debt conversion price | $ / shares	$ 39.78
Shares that would be issued upon conversion | shares	14.5

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- Definition

Antidilution adjustments of convertible note hedges.

+ References

No definition available.

+ Details

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Namespace Prefix:	ter_
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Balance Type:	na
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- Definition

Net Income (Loss) Per Common Share [Line Items]

+ References

No definition available.

+ Details

Name:	ter_NetIncomeLossPerCommonShareLineItems
Namespace Prefix:	ter_
Data Type:	xbrli:stringItemType
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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031898-161870

+ Details

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X

- Details

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