Employee Stock and Incentive Plans - Share-Based Compensation Expense (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Share-Based Compensation Expense [Line Items] | |||
| Share-Based Compensation Expense | $ 3.1 | $ 3.2 | $ 3.1 |
| Income Tax Benefit | 0.9 | 0.9 | 0.9 |
| Capitalized Share-Based Compensation Costs | $ 0.0 | 0.0 | 0.0 |
| Performance Shares [Member] | |||
| Share-Based Compensation Expense [Line Items] | |||
| Performance Period (Years) | 3 years | ||
| Share-Based Compensation Expense | $ 2.3 | 2.3 | 2.1 |
| Unrecognized Compensation Cost | $ 2.2 | ||
| Weighted-Average Period for Recognition (Years/Months) | 1 year 7 months 6 days | ||
| Restricted Stock Units [Member] | |||
| Share-Based Compensation Expense [Line Items] | |||
| Performance Period (Years) | 3 years | ||
| Share-Based Compensation Expense | $ 0.8 | $ 0.9 | $ 1.0 |
| Unrecognized Compensation Cost | $ 0.9 | ||