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Employee Incentive Plans - Summary of Non-Cash Compensation Expense under LTI Programs (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Total non-cash compensation expense | $ 9.6 | $ 9.7 | $ 10.1
Restricted Stock And Restricted Stock Units |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Total non-cash compensation expense | 6.1 | 6.1 | 5.8
Performance Shares |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Total non-cash compensation expense | $ 3.5 | $ 3.6 | $ 4.3

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