Name:	ntri_ContractualCommitmentsAbstract
Namespace Prefix:	ntri_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Carrying value of capitalized payments made in advance for inventory to be received in the future.

+ References

No definition available.

+ Details

Name:	ntri_CurrentAndNonCurrentAdvancesOnInventoryPurchases
Namespace Prefix:	ntri_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Specifies the maximum time period covered by the arrangement.

+ References

No definition available.

+ Details

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

- Definition

The value of recorded impairment on advances for inventory purchases to supplier which is in default with its lender.

+ References

No definition available.

+ Details

Name:	ntri_RecordedImpairmentOnInventoryPurchasesToSupplierInLenderDefault
Namespace Prefix:	ntri_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Term of the lessee's leasing arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Definition

Minimum amount of purchase arrangement in which the entity has agreed to expend funds to procure goods or services from a supplier.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

COMMITMENTS AND CONTINGENCIES (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Leases [Line Items]
Total rent expense	$ 2,237us-gaap_LeaseAndRentalExpense	$ 2,261us-gaap_LeaseAndRentalExpense	$ 4,807us-gaap_LeaseAndRentalExpense
Contractual Commitments
Maximum term of supply agreements with various food vendors (in Duration)	5 years
Purchase obligations	54,445us-gaap_PurchaseObligation
Advance payments made to suppliers			690
Impairment of supplier advance	$ 0	$ 0	$ 2,100
Minimum [Member]
Operating Leases [Line Items]
Lease obligations, term (in Duration)	1 year
Maximum [Member]
Operating Leases [Line Items]
Lease obligations, term (in Duration)	12 years