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Business Information - Additional Information (Details)
$ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
Segment
Entity
Dec. 31, 2018
USD ($)
Entity
Dec. 31, 2017
Entity
Segment Reporting Information [Line Items]      
Number of business segments (segment) | Segment 1    
United States      
Segment Reporting Information [Line Items]      
Long-lived assets | $ $ 22.8 $ 26.7  
Revenue | Geographic Concentration Risk | United States      
Segment Reporting Information [Line Items]      
Percentage of revenue 67.00% 52.00% 70.00%
Revenue | Geographic Concentration Risk | United Kingdom      
Segment Reporting Information [Line Items]      
Percentage of revenue 12.00% 29.00% 15.00%
Revenue | Customer Concentration Risk      
Segment Reporting Information [Line Items]      
Percentage of revenue 11.00%    
Number of clients that accounted for more than 10% of total revenues (entity) 1    
Advisory Services      
Segment Reporting Information [Line Items]      
Number of clients that accounted for more than 10% of total revenues (entity)   0 0