Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue Recognition
External freight billed to customers included in revenue	$ 6.8	$ 5.9	$ 12.7	$ 12.0

Represents fees charged to customers for the delivery, generally by postal or freight service providers, of product or goods purchased.

No definition available.

Name:	uslm_ShippingAndHandlingRevenues
Namespace Prefix:	uslm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration