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Net (Loss) Income Per Common Share - Additional Information (Detail) - shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Net Income Loss Per Common Share
Exercise of stock options	0.1	0.2

X

- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	ter_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Stock issued during period shares sale of stock and exercise of stock options.

+ References

No definition available.

+ Details

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Namespace Prefix:	ter_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration