Consolidated Statements of Shareholders’ Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balances at 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	6.4				6.4
Other comprehensive income (loss)	0.1					0.1
Excercise of stock options	3.3			3.3
Share-based compensation	6.3			6.3
Balances at end 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	55.5				55.5
Other comprehensive income (loss)	(8.6)					(8.6)
Excercise of stock options	1.9			1.9
Share-based compensation	6.6			6.6
Balances at end of period at Sep. 30, 2018	505.3	0.2	(46.3)	267.5	317.0	(33.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	85.1				85.1
Other comprehensive income (loss)	(1.7)					(1.7)
Excercise of stock options	1.2			1.2
Share-based compensation	8.1			8.1
Repurchase of stock	(3.8)		3.8
Balances at end of period at Sep. 30, 2019	$ 594.2	$ 0.2	$ (50.1)	$ 276.8	$ 402.1	$ (34.8)