| Document and Entity Information | Aug. 04, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 4, 2020 |
| Entity Registrant Name | GENTHERM Inc |
| Entity Central Index Key | 0000903129 |
| Entity Emerging Growth Company | false |
| Entity File Number | 0-21810 |
| Entity Incorporation State Country Code | MI |
| Entity Tax Identification Number | 95-4318554 |
| Entity Address, Address Line One | 21680 Haggerty Road |
| Entity Address, City or Town | Northville |
| Entity Address, State or Province | MI |
| Entity Address, Postal Zip Code | 48167 |
| City Area Code | (248) |
| Local Phone Number | 504-0500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, no par value |
| Trading Symbol | THRM |
| Security Exchange Name | NASDAQ |
