Assets and Liabilities Held for Sale - Summary of Assets and Liabilities of Disposal Group Classified as Held for Sale (Detail) (Parenthetical) $ in Thousands	Sep. 30, 2018 USD ($)
Discontinued Operations And Disposal Groups [Abstract]
Allowance for accounts receivable	$ 89

Allowance for doubtful accounts discontinued operations.

No definition available.

Name:	thrm_AllowanceForDoubtfulAccountsDiscontinuedOperations
Namespace Prefix:	thrm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant