Stock-Based Compensation Expense (Details) - USD ($) $ 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] | |||
Maximum number of shares reserved for grants | 6,555,000 | ||
Stock-based compensation expense [Abstract] | |||
Stock-based compensation expense | $ 9.4 | $ 10.0 | $ 9.3 |
Less: related tax benefit | 2.0 | 2.1 | 2.0 |
Net stock-based compensation expense | 7.4 | 7.9 | 7.3 |
Stock Option [Member] | |||
Stock-based compensation expense [Abstract] | |||
Stock-based compensation expense | 0.0 | 0.1 | 0.3 |
Restricted stock units (RSUs) | |||
Stock-based compensation expense [Abstract] | |||
Stock-based compensation expense | 3.0 | 2.7 | 2.5 |
Performance shares units [Member] | |||
Stock-based compensation expense [Abstract] | |||
Stock-based compensation expense | $ 6.4 | $ 7.2 | $ 6.5 |