Revenue Recognition - Summary of Disaggregated Net Sales (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Disaggregation Of Revenue [Line Items]
Net Sales	$ 238,147	$ 229,262	$ 465,409	$ 450,887
U.S. Customers [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	223,025	215,493	433,451	424,075
Non-U.S. Customers [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	15,122	13,769	31,958	26,812
Powertrain [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	99,224	95,365	194,375	190,228
Chassis [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	70,266	60,722	137,264	116,206
Automotive Body [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	57,289	61,530	112,534	123,004
Hardware [Member]
Disaggregation Of Revenue [Line Items]
Net Sales	$ 11,368	$ 11,645	$ 21,236	$ 21,449