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Concentration Risk - Schedule of Revenue Concentration (Details) - Product Concentration Risk
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Equity Assets    
Concentration Risk [Line Items]    
Concentration risk 40.00% 39.00%
Money Market Assets    
Concentration Risk [Line Items]    
Concentration risk 38.00% 40.00%
Fixed-Income Assets    
Concentration Risk [Line Items]    
Concentration risk 14.00% 17.00%