Summary of Significant Accounting Policies - Foreign Currency Translation (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Foreign Currency Transaction Gain (Loss), before Tax [Abstract]
Foreign currency transaction and remeasurement losses	$ (2.0)	$ (0.6)	$ 2.7	$ 0.6

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

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