Debt instrument maturity month and year range end.

No definition available.

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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

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Namespace Prefix:	thrm_
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Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility increase in maximum borrowing capacity.

+ References

No definition available.

+ Details

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Namespace Prefix:	thrm_
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Balance Type:	credit
Period Type:	instant

- Definition

Percentage of stock interest on subsidiaries pledge to secure obligation.

+ References

No definition available.

+ Details

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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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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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before accumulated amortization, of debt issuance costs related to line of credit arrangements. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section S45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68176171&loc=SL68176184-208336

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 210
-SubTopic 10
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+ Details

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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

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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

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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- Details

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Debt - Additional Information (Detail) - USD ($)			1 Months Ended	9 Months Ended	12 Months Ended
Debt - Additional Information (Detail) - USD ($)	Jun. 27, 2019	Jun. 26, 2019	Jan. 31, 2021	Dec. 31, 2020	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Aug. 07, 2014
Debt Instrument [Line Items]
Maximum percentage of stock of non US subsidiaries pledge to secure obligation				66.00%	66.00%
Amended credit agreement, debt issuance costs				$ 1,278,000	$ 1,278,000
Federal Funds Rate \| Minimum
Debt Instrument [Line Items]
Interest rate					0.50%
Federal Funds Rate \| Maximum
Debt Instrument [Line Items]
Interest rate					0.09%
London Interbank Offered Rate
Debt Instrument [Line Items]
Interest rate					0.14%
United State Bank Of America Credit Facility
Debt Instrument [Line Items]
Interest rate					3.25%
Euro Currency Rate Loans
Debt Instrument [Line Items]
Interest rate					1.00%
Euro Currency Rate Loans \| Credit Agreement \| Minimum
Debt Instrument [Line Items]
Interest rate					1.25%
Euro Currency Rate Loans \| Credit Agreement \| Maximum
Debt Instrument [Line Items]
Interest rate					2.25%
Base Rate Loans \| Credit Agreement \| Minimum
Debt Instrument [Line Items]
Interest rate					0.25%
Base Rate Loans \| Credit Agreement \| Maximum
Debt Instrument [Line Items]
Interest rate					1.25%
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 \| Revolving Note (U.S. Dollar)
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 475,000,000	$ 350,000,000						$ 350,000,000
Line of credit, outstanding amount				186,184,000	$ 186,184,000
Debt maturity date	Jun. 27, 2024	Mar. 17, 2021
Increase in maximum borrowing capacity						$ 169,546,000
Remaining borrowing capacity				288,776,000	288,776,000
Line of credit, repayment amount				41,180,000
Revolving Credit Facility \| Revolving Note (U.S. Dollar) \| Subsequent Event
Debt Instrument [Line Items]
Line of credit, repayment amount			$ 80,000,000
Revolving Credit Facility \| Revolving Note (U.S. Dollar) \| Letters of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity				15,000,000	15,000,000
Line of credit, outstanding amount				0	0		$ 0
Revolving Credit Facility \| Revolving Note (U.S. Dollar) \| Swing Line Loans
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 40,000,000	$ 40,000,000