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

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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
Balance Type: | na
Period Type: | duration

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- Definition Stock issued during period shares sale of stock and exercise of stock options. + References No definition available. + Details
Name: | ter_StockIssuedDuringPeriodSharesSaleOfStockAndExerciseOfStockOptions
Namespace Prefix: | ter_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration