Earnings (Loss) Per Share of Common Stock - Reconciliation of Numerator and Denominator for Basic and Diluted Earnings (loss) Per Share Calculation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income (loss)	$ 6.3	$ (20.5)	$ (5.7)	$ (33.1)
Weighted average number of common shares outstanding – basic	105,183,000	103,651,000	105,165,000	103,478,000
Basic income (loss) per share	$ 0.06	$ (0.20)	$ (0.05)	$ (0.32)
Weighted average number of common shares outstanding – diluted	105,670,000	103,651,000	105,165,000	103,478,000
Diluted income (loss) earnings per share	$ 0.06	$ (0.20)	$ (0.05)	$ (0.32)
Weighted average number of anti-dilutive options and restricted stock	7,719,000	8,453,000	7,754,000	8,030,000