Discontinued Operations Discontinued Operations - Cequent Spin-off (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2015	Sep. 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
Cash distribution received from Cequent spin-off	$ 214,500
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	0	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	$ 0	$ 155,160