Summary of Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Accounting Policies [Abstract]
Goodwill, gross	$ 180.7	$ 180.7
Accumulated impairment losses	(114.8)	(114.8)
Goodwill	$ 65.9	$ 65.9

Amount, after accumulated impairment loss, of asset representing future economic benefit arising from other asset acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized.

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+ Details