Revenue Recognition - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Deferred revenue, revenue recognized	$ 39.4
Cumulative catch-up adjustment to revenue from change in estimates	(10.9)
Contractual retainage provisions	11.5	$ 13.4
Performance-based \| Transferred over Time
Disaggregation of Revenue [Line Items]
Unbilled accounts receivable	47.0
Future Outcomes \| Performance-based \| Transferred over Time
Disaggregation of Revenue [Line Items]
Deferred revenue, revenue recognized	91.3
Average Effective Rate \| Performance-based \| Transferred over Time
Disaggregation of Revenue [Line Items]
Deferred revenue, revenue recognized	$ 144.0

Amount billed to customers under long-term contracts or programs that have been withheld because of retainage provisions in a contract.

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