Segment Information About Reported Segment Product Revenues by Product Category (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Product revenues	$ 257,921	$ 264,586
Percentage change	(2.50%)
Automotive Segments
Segment Reporting Information [Line Items]
Product revenues	$ 242,357	242,421
Automotive Segments | Climate Control Seat (CCS)
Segment Reporting Information [Line Items]
Product revenues	$ 94,354	88,218
Percentage change	7.00%
Automotive Segments | Seat Heaters
Segment Reporting Information [Line Items]
Product revenues	$ 73,920	84,220
Percentage change	(12.20%)
Automotive Segments | Steering Wheel Heaters
Segment Reporting Information [Line Items]
Product revenues	$ 16,970	17,557
Percentage change	(3.30%)
Automotive Segments | Automotive Cables
Segment Reporting Information [Line Items]
Product revenues	$ 23,749	26,865
Percentage change	(11.60%)
Automotive Segments | Battery Thermal Management (BTM)
Segment Reporting Information [Line Items]
Product revenues	$ 10,745	4,161
Percentage change	158.20%
Automotive Segments | Electronics
Segment Reporting Information [Line Items]
Product revenues	$ 12,852	15,188
Percentage change	(15.40%)
Automotive Segments | Other Automotive
Segment Reporting Information [Line Items]
Product revenues	$ 9,767	6,212
Percentage change	57.20%
Industrial Segments
Segment Reporting Information [Line Items]
Product revenues	$ 15,564	22,165
Percentage change	(29.80%)
Industrial Segments | Remote Power Generation
Segment Reporting Information [Line Items]
Product revenues	$ 3,959	4,662
Percentage change	(15.10%)
Industrial Segments | Industrial Chambers
Segment Reporting Information [Line Items]
Product revenues	$ 3,418	10,213
Percentage change	(66.50%)
Industrial Segments | Gentherm Medical
Segment Reporting Information [Line Items]
Product revenues	$ 8,187	$ 7,290
Percentage change	12.30%