Inventory (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Inventory Disclosure [Abstract]
Cost of goods sold, amortization of operating materials	$ 1.1	$ 1.0

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