Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Jul. 25, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	THRM
Entity Registrant Name	GENTHERM INC
Entity Central Index Key	0000903129
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		32,982,600
Entity Shell Company	false
Entity File Number	0-21810
Entity Tax Identification Number	954318554
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