Summary of Significant Accounting Policies - Foreign Currency Translation (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Foreign Currency Transaction Gain (Loss), before Tax [Abstract]
Foreign currency transaction and remeasurement losses	$ (1.8)	$ (3.4)	$ (1.8)

Amount before tax of foreign currency transaction realized gain (loss) recognized in the income statement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124440516&loc=d3e30840-110895

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=125521441&loc=d3e30690-110894

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration