Stock-Based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
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	$ 9.1	$ 9.4	$ 10.0
Less: related tax benefit	1.8	2.0	2.1
Net stock-based compensation expense	$ 7.3	7.4	7.9
% of Shares Subject to Forfeiture	0.00%
Maximum Percentage of Shares Subject to Forfeiture	15.00%
Stock Option [Member]
Stock-based compensation expense [Abstract]
Stock-based compensation expense	$ 0.0	0.0	0.1
Restricted stock units (RSUs)
Stock-based compensation expense [Abstract]
Stock-based compensation expense	3.4	3.0	2.7
Performance shares units [Member]
Stock-based compensation expense [Abstract]
Stock-based compensation expense	$ 5.7	$ 6.4	$ 7.2

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Stock-based compensation expense [Abstract]

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

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Amount, after tax, of expense for 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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Number of shares authorized for issuance under share-based payment arrangement.

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