Quarterly report pursuant to Section 13 or 15(d)

Revenue Recognition - Narrative (Details)

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Revenue Recognition - Narrative (Details)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
segment
product_category
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]          
Retained earnings (accumulated deficit) $ 844   $ 844   $ (2,072)
Decrease in revenue (88,828) $ (89,301) (267,436) $ (253,743)  
Decrease in operating income (3,513) (2,154) $ (6,580) (4,228)  
Refund period     90 days    
Number of principal categories of products | product_category     6    
Number of business segments | segment     4    
NSP Americas; NSP Russia, Central and Eastern Europe; and NSP China          
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]          
Number of operating segments | segment     3    
Synergy WorldWide          
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]          
Decrease in revenue $ (34,497) $ (34,470) $ (103,034) $ (92,146)  
Number of operating segments | segment     1    
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606          
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]          
Retained earnings (accumulated deficit)         $ 900
Decrease in revenue     $ 500    
Decrease in operating income     $ 200