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Stock-Based Compensation - Stock-based Compensation Expense by Award Type and Expense Category (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Feb. 03, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total stock-based compensation expense (credit) | $ 36.1 | $ 25.1 |
Cost of services and product development |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total stock-based compensation expense (credit) | 13.7 | 12.1 |
Selling, general and administrative |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total stock-based compensation expense (credit) | 22.4 | 13.0 |
Stock appreciation rights |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total stock-based compensation expense (credit) | 2.0 | 1.7 |
Restricted stock units |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total stock-based compensation expense (credit) | 33.9 | 23.2 |
Common stock equivalents |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total stock-based compensation expense (credit) | 0.2 | 0.2 |
Retirement eligible employees equity award |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total stock-based compensation expense (credit) | $ 21.5 | $ 11.6 |
Performance-based RSUs | Executive officer |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Target performance percentage | 50.00% |  | 95.00%
Total stock-based compensation expense (credit) | $ 6.5 |  |

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