Discontinued Operations Discontinued Operations - Cequent Spin-off (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Horizon Shares Received in Spin-off		2
TriMas Number of Common Shares Held		5
Cash distribution received from Cequent spin-off	$ 214,500	$ 214,500
Cequent businesses [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Assets			$ 0	$ 0
Disposal Group, Including Discontinued Operation, Liabilities			$ 0	$ 0