Fair Value Measures (Narrative) (Details) - USD ($)	Mar. 31, 2018	Dec. 30, 2017
Fair Value Measures [Abstract]
Transfers of financial assets or liabilities	$ 0	$ 0
Non-financial assets	$ 0	$ 0

Fair Value, Assets And Liabilities, Level 1 Between Level 2 Transfers, Amount

No definition available.

Name:	usna_FairValueAssetsAndLiabilitiesLevel1BetweenLevel2TransfersAmount
Namespace Prefix:	usna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant