Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue Recognition
External freight billed to customers included in revenue	$ 8.0	$ 7.7	$ 21.3	$ 21.7

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