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Segment Information (Narrative) (Details)	3 Months Ended
	Mar. 30, 2019 item segment
Segment Information [Abstract]
Number of reportable segments | segment	1
Percentage of revenue from major customers, maximum	10.00%
Geographic regions	2
Sub-geographical regions	3

X

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

Name:	us-gaap_SegmentReportingAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Number Of Geographic Regions

+ References

No definition available.

+ Details

Name:	usna_NumberOfGeographicRegions
Namespace Prefix:	usna_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Number Of Sub Geographical Regions

+ References

No definition available.

+ Details

Name:	usna_NumberOfSubGeographicalRegions
Namespace Prefix:	usna_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Percentage Of Revenue From Major Customer

+ References

No definition available.

+ Details

Name:	usna_PercentageOfRevenueFromMajorCustomer
Namespace Prefix:	usna_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration