Subsequent Event (Notes)	12 Months Ended
Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events [Text Block]	16. Subsequent Events On January 16, 2018, 1137925 B.C. Ltd. (the “Subsidiary”), a wholly owned subsidiary of Core Molding Technologies, Inc. (the “Company”), entered into an Asset Purchase Agreement (the “Agreement”) with Horizon Plastics International Inc., 1541689 Ontario Inc., 2551024 Ontario Inc. and Horizon Plastics de Mexico, S.A. de C.V. (collectively “Horizon Plastics”). Pursuant to the terms of the Agreement the Company acquired substantially all of the assets and assumed certain specified liabilities of Horizon Plastics in exchange for approximately $63,000,000 in cash, subject to a working capital closing adjustment. The initial accounting for the business combination was not complete at the time the financial statements were issued due to the timing of the acquisition and the filing of this Annual Report on Form 10-K. As a result, disclosures required under ASC 805-10-50, Business Combinations, cannot be made at this time. The acquisition was funded through a combination of available cash on hand and borrowings under the Amended and Restated Credit Agreement ("A/R Credit Agreement") entered in to on January 16, 2018 with KeyBank National Association as administrative agent and the various financial institutions party thereto as lenders (the "lenders"). Pursuant to the terms of the A/R Credit Agreement (i) the Company may borrow revolving loans in the aggregate principal amount of up to $40,000,000 (the “US Revolving Loans”) from the Lenders and term loans in the aggregate principal amount of up to $32,000,000 from the Lenders, (ii) the Subsidiary may borrow revolving loans in an aggregate principal amount of up to $10,000,000 from the Lenders (which revolving loans shall reduce the availability of the US Revolving Loans to the Company on a dollar-for-dollar basis) and term loans in an aggregate principal amount of up to $13,000,000 from the Lenders and (iii) the Company may increase the aggregate principal amount of the aforementioned loans by up to an additional$25,000,000. On January 16, 2018, the Company entered into two interest rate swap agreements that became effective January 18, 2018 and continues through January 2023, one of which was designated as a cash flow hedge for $25,000,000 of the $32,000,000 term loan to the Company mentioned above and the other was designated as a cash flow hedge for $10,000,0000 of the $13,000,000 term loan to the Subsidiary mentioned above. Under these agreements, the Company will pay a fixed rate of 4.58% to the counterparty and receives daily LIBOR.

16. Subsequent Events

On January 16, 2018, 1137925 B.C. Ltd. (the “Subsidiary”), a wholly owned subsidiary of Core Molding Technologies, Inc. (the “Company”), entered into an Asset Purchase Agreement (the “Agreement”) with Horizon Plastics International Inc., 1541689 Ontario Inc., 2551024 Ontario Inc. and Horizon Plastics de Mexico, S.A. de C.V. (collectively “Horizon Plastics”). Pursuant to the terms of the Agreement the Company acquired substantially all of the assets and assumed certain specified liabilities of Horizon Plastics in exchange for approximately $63,000,000 in cash, subject to a working capital closing adjustment. The initial accounting for the business combination was not complete at the time the financial statements were issued due to the timing of the acquisition and the filing of this Annual Report on Form 10-K. As a result, disclosures required under ASC 805-10-50, Business Combinations, cannot be made at this time.

The acquisition was funded through a combination of available cash on hand and borrowings under the Amended and Restated Credit Agreement ("A/R Credit Agreement") entered in to on January 16, 2018 with KeyBank National Association as administrative agent and the various financial institutions party thereto as lenders (the "lenders"). Pursuant to the terms of the A/R Credit Agreement (i) the Company may borrow revolving loans in the aggregate principal amount of up to $40,000,000 (the “US Revolving Loans”) from the Lenders and term loans in the aggregate principal amount of up to $32,000,000 from the Lenders, (ii) the Subsidiary may borrow revolving loans in an aggregate principal amount of up to $10,000,000 from the Lenders (which revolving loans shall reduce the availability of the US Revolving Loans to the Company on a dollar-for-dollar basis) and term loans in an aggregate principal amount of up to $13,000,000 from the Lenders and (iii) the Company may increase the aggregate principal amount of the aforementioned loans by up to an additional$25,000,000.

On January 16, 2018, the Company entered into two interest rate swap agreements that became effective January 18, 2018 and continues through January 2023, one of which was designated as a cash flow hedge for $25,000,000 of the $32,000,000 term loan to the Company mentioned above and the other was designated as a cash flow hedge for $10,000,0000 of the $13,000,000 term loan to the Subsidiary mentioned above. Under these agreements, the Company will pay a fixed rate of 4.58% to the counterparty and receives daily LIBOR.