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Customer Trust Fund - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Investment income from invested customer trust fund included in revenue $ 52.3 $ 80.2 $ 67.0
Maturities ranging from one to 120 days [Member]      
Average customer trust funds held in liquidity portfolios, Percentage 49.00%    
Maturities ranging from 120 days to 10 years [Member]      
Average customer trust funds held in fixed income portfolios, Percentage 51.00%