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Commitments and Contingencies - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2019 Agreement
Loss Contingencies [Line Items] |
Number of agreements expire in 2020 | 0
Labor Agreements |
Loss Contingencies [Line Items] |
Percentage of workforce as members of industrial trade unions | 25.00%

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- Definition Number of agreements expire. + References No definition available. + Details
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Namespace Prefix: | thrm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of workforce as members of industrial trade unions. + References No definition available. + Details
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Namespace Prefix: | thrm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |