Annual report pursuant to Section 13 and 15(d)

OPERATING BUSINESS SEGMENT AND INTERNATIONAL OPERATION INFORMATION (Narrative) (Details) (Details)

v3.10.0.1
OPERATING BUSINESS SEGMENT AND INTERNATIONAL OPERATION INFORMATION (Narrative) (Details) (Details)
$ in Millions
12 Months Ended
Dec. 31, 2018
USD ($)
segment
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Segment Reporting Information [Line Items]      
Number of business segments 4    
Selling, General and Administrative Expenses      
Segment Reporting Information [Line Items]      
Service fees | $ $ 11.5 $ 7.2 $ 4.3
NSP Americas; NSP Russia, Central and Eastern Europe; and NSP China      
Segment Reporting Information [Line Items]      
Number of operating segments 3    
Synergy WorldWide      
Segment Reporting Information [Line Items]      
Number of operating segments 1