Major Customers (Details) - USD ($)	3 Months Ended		9 Months Ended
Major Customers (Details) - USD ($)	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue, Major Customer [Line Items]
Net sales	$ 59,873,000	$ 74,655,000	$ 161,705,000	$ 228,168,000
Product [Member]
Revenue, Major Customer [Line Items]
Net sales	54,240,000	67,511,000	152,019,000	214,403,000
Tooling [Member]
Revenue, Major Customer [Line Items]
Net sales	5,633,000	7,144,000	9,686,000	13,765,000
Navistar [Member]
Revenue, Major Customer [Line Items]
Net sales	13,263,000	15,260,000	31,615,000	47,338,000
Navistar [Member] \| Product [Member]
Revenue, Major Customer [Line Items]
Net sales	8,065,000	15,115,000	25,231,000	46,411,000
Navistar [Member] \| Tooling [Member]
Revenue, Major Customer [Line Items]
Net sales	5,198,000	145,000	6,384,000	927,000
Volvo [Member]
Revenue, Major Customer [Line Items]
Net sales	4,945,000	11,178,000	16,833,000	40,413,000
Volvo [Member] \| Product [Member]
Revenue, Major Customer [Line Items]
Net sales	4,907,000	11,117,000	14,647,000	40,213,000
Volvo [Member] \| Tooling [Member]
Revenue, Major Customer [Line Items]
Net sales	38,000	61,000	2,186,000	200,000
Universal Forest Products [Member]
Revenue, Major Customer [Line Items]
Net sales	12,188,000	6,751,000	30,659,000	22,076,000
Universal Forest Products [Member] \| Product [Member]
Revenue, Major Customer [Line Items]
Net sales	12,188,000	6,751,000	30,659,000	22,076,000
Universal Forest Products [Member] \| Tooling [Member]
Revenue, Major Customer [Line Items]
Net sales	0	0	0	0
Paccar [Member]
Revenue, Major Customer [Line Items]
Net sales	8,447,000	11,697,000	19,769,000	37,104,000
Paccar [Member] \| Product [Member]
Revenue, Major Customer [Line Items]
Net sales	8,268,000	11,532,000	19,383,000	35,779,000
Paccar [Member] \| Tooling [Member]
Revenue, Major Customer [Line Items]
Net sales	179,000	165,000	386,000	1,325,000
BRP [Member]
Revenue, Major Customer [Line Items]
Net sales	4,415,000	5,618,000	14,201,000	14,645,000
BRP [Member] \| Product [Member]
Revenue, Major Customer [Line Items]
Net sales	4,240,000	3,116,000	13,693,000	11,287,000
BRP [Member] \| Tooling [Member]
Revenue, Major Customer [Line Items]
Net sales	175,000	2,502,000	508,000	3,358,000
Other Customers [Member]
Revenue, Major Customer [Line Items]
Net sales	16,615,000	24,151,000	48,628,000	66,592,000
Other Customers [Member] \| Product [Member]
Revenue, Major Customer [Line Items]
Net sales	16,572,000	19,880,000	48,406,000	58,637,000
Other Customers [Member] \| Tooling [Member]
Revenue, Major Customer [Line Items]
Net sales	$ 43,000	$ 4,271,000	$ 222,000	$ 7,955,000