Stock-Based Compensation Plans - Narrative (Details) $ in Millions		3 Months Ended		6 Months Ended
	Jul. 01, 2022 shares	Jun. 30, 2025 USD ($) plan shares	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($) plan shares	Jun. 30, 2024 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense for share-based payments		$ 7.6	$ 11.0	$ 16.3	$ 21.5
Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total grants in period (in shares) | shares				12,415,445
Shares issued under the omnibus plan (in shares) | shares				34,508,688
Number of shares authorized (in shares) | shares		45,000,000		45,000,000
Employee Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost		$ 4.8		$ 4.8
Employee Stock Option Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting period				1 year
Option expiration period				5 years
Employee Stock Option Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option vesting period				5 years
Option expiration period				10 years
Restricted Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost		56.1		$ 56.1
Restricted period, maximum				10 years
Amortization expense		$ 5.0	6.9	$ 10.9	13.6
Gentex Corporation Employee Stock Purchase Plan | Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under the omnibus plan (in shares) | shares				673,245
Number of shares authorized (in shares) | shares	2,000,000
ESPP discount rate	85.00%
ESPP discount rate recognized as compensation expense	15.00%
Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of plans | plan		2		2
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense for share-based payments		$ 0.9	2.0	$ 2.0	3.8
Unrecognized compensation cost		13.1		$ 13.1
Performance Shares | Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under the omnibus plan (in shares) | shares				5,115,466
Performance Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense for share-based payments		$ 0.5	$ 0.4	$ 0.9	$ 0.9
Option vesting period				4 years