Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss, net
Balance at beginning 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	18.2				18.2
Other comprehensive income	0.3					0.3
Exercise of stock options	0.3			0.3
Share-based Compensation	1.9			1.9
Repurchase of common stock	0.0
Balance at end of period at Dec. 31, 2018	526.0	0.2	46.3	269.7	335.2	(32.8)
ASU 2018-02 cumulative transition adjustment	0.7				0.7	(0.7)
Adjusted Balances	594.2	0.2	(50.1)	276.8	402.8	(35.5)
Balance at beginning of period at Sep. 30, 2019	594.2	0.2	(50.1)	276.8	402.1	(34.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16.3				16.3
Other comprehensive income	0.7					0.7
Exercise of stock options	1.5			1.5
Share-based Compensation	2.6			2.6
Repurchase of common stock	(0.4)		0.4
Balance at end of period at Dec. 31, 2019	$ 614.9	$ 0.2	$ (50.5)	$ 280.9	$ 419.1	$ (34.8)