Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Revenue Recognition
External freight billed to customers included in revenue	$ 7.8	$ 6.9

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