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 the credit facility terminates, in CCYY-MM-DD format.

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

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

- 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_StatementScenarioAxis=us-gaap_ScenarioForecastMember
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:

Debt - Additional Information (Detail) - USD ($)		3 Months Ended	6 Months Ended
Debt - Additional Information (Detail) - USD ($)	Mar. 17, 2016	Mar. 31, 2016	Sep. 30, 2016	Mar. 16, 2016
Debt Instrument [Line Items]
Maximum percentage of stock of non US subsidiaries pledge to secure obligation	66.00%
Revolving Note
Debt Instrument [Line Items]
Line of credit facility, due date		Mar. 17, 2021
Federal Funds Rate \| Minimum
Debt Instrument [Line Items]
Interest rate		0.25%
Federal Funds Rate \| Maximum
Debt Instrument [Line Items]
Interest rate		0.50%
London Interbank Offered Rate
Debt Instrument [Line Items]
Interest rate		0.38%
Revolving Note (U.S. Dollar)
Debt Instrument [Line Items]
Aggregate principal amount available for borrowing	$ 250,000,000			$ 100,000,000
United State Bank Of America Credit Facility
Debt Instrument [Line Items]
Interest rate		3.50%
Euro Currency Rate Loans \| Scenario, Forecast
Debt Instrument [Line Items]
Interest rate			1.50%
Euro Currency Rate Loans \| Minimum
Debt Instrument [Line Items]
Interest rate	1.25%	0.00%
Euro Currency Rate Loans \| Maximum
Debt Instrument [Line Items]
Interest rate	2.00%	1.00%
Base Rate Loans \| Scenario, Forecast
Debt Instrument [Line Items]
Interest rate			0.50%
Base Rate Loans \| Minimum
Debt Instrument [Line Items]
Interest rate	0.25%
Base Rate Loans \| Maximum
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