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Revenue from Contracts with Customers - Additional Information (Detail) - Agreement
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disaggregation of Revenue [Line Items]      
Percentage of billing expense revenues 2.00%    
Sales Revenue Net [Member] | Revenue from Rights Concentration Risk [Member] | CGI [Member]      
Disaggregation of Revenue [Line Items]      
Percentage of total accounts receivable 15.00% 11.30% 12.80%
Number of customers 1 1 1
Accounts Receivable [Member] | Revenue from Rights Concentration Risk [Member] | CGI [Member]      
Disaggregation of Revenue [Line Items]      
Percentage of total accounts receivable 11.70% 10.30%  
Top Ten Customers [Member]      
Disaggregation of Revenue [Line Items]      
Revenue percentage of total revenue 47.00% 45.00% 47.00%
Data and Analytics Services [Member]      
Disaggregation of Revenue [Line Items]      
Percent of revenue from services     100.00%