Condensed Consolidated Statement of Stockholders' Equity - 6 months ended Mar. 31, 2017 - 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, 2016	$ 433.8	$ 0.2	$ (46.3)	$ 249.4	$ 255.1	$ (24.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17.3				17.3
Other comprehensive loss	(0.2)					(0.2)
Exercise of stock options	2.2			2.2
Share-based Compensation	2.6			2.6
Balances as of end of period at Mar. 31, 2017	$ 455.7	$ 0.2	$ (46.3)	$ 254.2	$ 272.4	$ (24.8)