COMMITMENTS AND CONTINGENCIES (Narrative) (Details)	3 Months Ended
Mar. 31, 2015
Contractual Commitments
Maximum term of supply agreements with various food vendors (in Duration)	5 years
Number of supply agreements which provide volume purchase rebates (in Integer)	1

Specifies the maximum time period covered by the arrangement.

No definition available.

Name:	ntri_LongTermPurchaseCommitmentMaximumTimePeriod
Namespace Prefix:	ntri_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration