STOCK-BASED COMPENSATION PLANS Grants on stock-based compensation awards during the period (Details) shares in Thousands	9 Months Ended
Sep. 30, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, granted in period (in shares)	2,298
Total share awards granted in period (in shares)	3,958
Time-based restricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-option stock awards, granted in period (in shares)	1,295
Market-based restricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-option stock awards, granted in period (in shares)	365

Share based Compensation Arrangement by Share based Payment Award, Grants in Period

No definition available.

Name:	gnc_SharebasedCompensationArrangementbySharebasedPaymentAwardGrantsinPeriod
Namespace Prefix:	gnc_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=gnc_TimebasedRestrictedStockAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=gnc_MarketbasedRestrictedStockAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: