Stock-Based Compensation - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 5.0	$ 5.9	$ 5.5
Tax benefit from compensation expense	1.2	1.5	1.7
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, compensation cost not yet recognized	$ 5.3
Share-based compensation, compensation cost not yet recognized, recognition period	2 years 2 months 12 days
Share-based compensation, fair value of vested awards	$ 0.9	$ 1.9	$ 1.9

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

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

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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