Condensed Consolidated Statement of Stockholders' Equity - 6 months ended Mar. 31, 2018 - USD ($) $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balances as of beginning of period at Sep. 30, 2017	$ 449.9	$ 0.2	$ (46.3)	$ 259.0	$ 261.5	$ (24.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15.8				15.8
Other comprehensive loss	(3.8)					(3.8)
Exercise of stock options	1.5			1.5
Share-based Compensation	3.2			3.2
Balances as of end of period at Mar. 31, 2018	$ 466.6	$ 0.2	$ (46.3)	$ 263.7	$ 277.3	$ (28.3)