Debt instrument maturity month and year range end.

No definition available.

Name:	thrm_DebtInstrumentMaturityMonthAndYearRangeEnd
Namespace Prefix:	thrm_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument maturity month and year range start.

+ References

No definition available.

+ Details

Name:	thrm_DebtInstrumentMaturityMonthAndYearRangeStart
Namespace Prefix:	thrm_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of stock interest on subsidiaries pledge to secure obligation.

+ References

No definition available.

+ Details

Name:	thrm_PercentageOfStockInterestOnSubsidiariesPledgeToSecureObligation
Namespace Prefix:	thrm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The effective interest rate during the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_FederalFundsEffectiveSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=thrm_UnitedStateRevolvingNoteMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=thrm_UnitedStateBankOfAmericaCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=thrm_EuroCurrencyRateLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=thrm_AmendedCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=thrm_BaseRateLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=thrm_DEGLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=thrm_DEGVietnamLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Additional Information (Detail) - USD ($)	9 Months Ended
Debt - Additional Information (Detail) - USD ($)	Sep. 30, 2017	Dec. 15, 2016	Dec. 14, 2016
Debt Instrument [Line Items]
Maximum percentage of stock of non US subsidiaries pledge to secure obligation		66.00%
Federal Funds Rate \| Minimum
Debt Instrument [Line Items]
Interest rate	0.50%
Federal Funds Rate \| Maximum
Debt Instrument [Line Items]
Interest rate	1.06%
London Interbank Offered Rate
Debt Instrument [Line Items]
Interest rate	1.23%
Revolving Note (U.S. Dollar)
Debt Instrument [Line Items]
Aggregate principal amount available for borrowing	$ 221,000
Letter of credit net of outstanding amount	$ 330,000
Debt maturity date	Mar. 17, 2021
United State Bank Of America Credit Facility
Debt Instrument [Line Items]
Interest rate	4.25%
Euro Currency Rate Loans \| Minimum
Debt Instrument [Line Items]
Interest rate	0.00%
Euro Currency Rate Loans \| Minimum \| Amended Credit Agreement
Debt Instrument [Line Items]
Interest rate	1.25%
Euro Currency Rate Loans \| Maximum
Debt Instrument [Line Items]
Interest rate	1.00%
Euro Currency Rate Loans \| Maximum \| Amended Credit Agreement
Debt Instrument [Line Items]
Interest rate	2.00%
Base Rate Loans \| Minimum \| Amended Credit Agreement
Debt Instrument [Line Items]
Interest rate	0.25%
Base Rate Loans \| Maximum \| Amended Credit Agreement
Debt Instrument [Line Items]
Interest rate	1.00%
DEG Loan
Debt Instrument [Line Items]
Semi-annual principal payments earliest date	2015-03
Semi-annual principal payments latest date	2019-09
DEG Vietnam Loan
Debt Instrument [Line Items]
Semi-annual principal payments earliest date	2017-11
Semi-annual principal payments latest date	2023-05
Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate principal amount available for borrowing		$ 350,000,000	$ 250,000,000