Discontinued Operations Discontinued Operations - Cequent Spin-off (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
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
Disposal Group, Including Discontinued Operation, Assets, Current	$ 0	$ 197,420
Disposal Group, Including Discontinued Operation, Liabilities, Current	0	119,900
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, Cash and Cash Equivalents	17,050	0
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net	92,750	63,520
Disposal Group, Including Discontinued Operation, Inventory, Current	125,750	123,370
Disposal Group, Including Discontinued Operation, Deferred Tax Asset, Current	4,840	4,840
Disposal Group, Including Discontinued Operation, Prepaid and Other Assets, Current	6,520	5,690
Disposal Group, Including Discontinued Operation, Assets, Current	246,910	197,420
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment, Noncurrent	48,870	55,180
Disposal Group, Including Discontinued Operation, Goodwill, Noncurrent	5,630	6,580
Disposal Group, Including Discontinued Operation, Intangible Assets, Noncurrent	61,400	66,510
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent	15,910	11,930
Disposal Group, Including Discontinued Operation, Assets	378,720	337,620
Disposal Group, Including Discontinued Operations, Debt, Current	17,940	460
Disposal Group, Including Discontinued Operation, Accounts Payable, Current	81,830	81,500
Disposal Group, Including Discontinued Operation, Accrued Liabilities, Current	44,190	37,940
Disposal Group, Including Discontinued Operation, Liabilities, Current	143,960	119,900
Disposal Group, Including Discontinued Operations, Debt, Noncurrent	195,460	300
Disposal Group, Including Discontinued Operation, Deferred Tax Liabilities, Noncurrent	9,220	8,970
Disposal Group, Including Discontinued Operation, Other Liabilities, Noncurrent	27,900	25,990
Disposal Group, Including Discontinued Operation, Liabilities	$ 376,540	$ 155,160