Subsequent Event (Details) - USD ($)	Jan. 16, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Long-term Debt		$ 6,750,000	$ 9,750,000
Core Molding Technologies, Inc. [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 40,000,000
Long-term Debt	32,000,000
Horizon [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	10,000,000
Business Acquisitions, Gross Purchase Price	63,000,000
Long-term Debt	$ 13,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.58%
Maximum [Member] | Horizon [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Long-term Debt	$ 25,000,000