Revenue Recognition - Summary of Disaggregated Net Sales (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Disaggregation Of Revenue [Line Items]
Net Sales	$ 300,620	$ 253,796	$ 791,532	$ 751,762
U.S. Customers [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	280,330	238,466	744,285	701,778
Non-U.S. Customers [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	20,290	15,330	47,247	49,984
Powertrain [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	120,565	104,756	323,396	299,730
Chassis [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	87,977	70,787	227,273	228,446
Automotive Body [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	74,445	65,468	197,624	189,174
Hardware [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	$ 17,633	$ 12,785	$ 43,239	$ 34,412