Inventory (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Inventory Disclosure [Abstract]
Cost of goods sold, amortization of operating materials	$ 1.5	$ 1.1

Cost of goods sold, amortization of operating materials.

No definition available.

Name:	usap_CostOfGoodsSoldAmortizationOfOperatingMaterials
Namespace Prefix:	usap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration