Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue Recognition
External freight billed to customers included in revenue	$ 7.8	$ 6.4	$ 21.7	$ 19.1

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