Employee Stock and Incentive Plans - Share-Based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-Based Compensation Expense [Line Items]
Share-Based Compensation Expense	$ 3.1	$ 3.1	$ 3.2
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	$ 2.2	2.3	2.3
Unrecognized Compensation Cost	$ 1.7
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	$ 0.9	$ 0.8	$ 0.9
Unrecognized Compensation Cost	$ 0.9
Weighted-Average Period for Recognition (Years/Months)	1 year 8 months 12 days

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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