Revenue from Contract with Customer - Additional Information (Detail) - Accounting Standards Update 2014-09 [Member] - Customer	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Percentage of billing expense revenues			2.00%
Sales Revenue Net [Member] | Revenue from Rights Concentration Risk [Member]
Disaggregation of Revenue [Line Items]
Number of customers	1	2	1	2
Sales Revenue Net [Member] | Revenue from Rights Concentration Risk [Member] | CGI [Member]
Disaggregation of Revenue [Line Items]
Percentage of number of customers revenue	13.50%	12.50%	12.90%	13.10%
Sales Revenue Net [Member] | Revenue from Rights Concentration Risk [Member] | Accenture PLC [Member]
Disaggregation of Revenue [Line Items]
Percentage of number of customers revenue		11.70%		10.50%
Top Ten Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue percentage of total revenue	48.00%	47.00%	48.00%	48.00%
Data and Analytics Services [Member]
Disaggregation of Revenue [Line Items]
Percentage of revenue from customers			100.00%