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Components of Net Periodic Pension Benefit Cost (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 101 $ 387 $ 379
Interest cost 111 98 80
Amortization of actuarial loss (gains)     27
Amortization of prior service cost 509    
Net periodic benefit cost 721 485 486
Gentherm GmbH      
Defined Benefit Plan Disclosure [Line Items]      
Interest cost 130 154 142
Return on plan assets (121) (125) (126)
Amortization of actuarial loss (gains) 78 48 59
Amortization of prior service cost     572
Net periodic benefit cost $ 87 $ 77 $ 647