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Compensation and Benefits - Pre-Offering Related Compensation (Details) - Unvested restricted share-based awards - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Forfeited (in dollars per share) $ 30.92 $ 34.61 $ 36.09
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount $ 76.4    
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition 3 years 1 month 6 days