Consolidated Statement Of Stockholders' Equity - USD ($) $ in Millions	Total	Common stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive income (loss)	Noncontrolling Interest [Member]	Stock-based Compensation Related [Member]	Stock-based Compensation Related [Member] Common stock	Stock-based Compensation Related [Member] Additional paid-in capital	Stock-based Compensation Related [Member] Accumulated deficit	Stock-based Compensation Related [Member] Accumulated other comprehensive income (loss)	Stock-based Compensation Related [Member] Noncontrolling Interest [Member]
Balance at Sep. 30, 2017	$ 489.5	$ 1.6	$ 1,494.2	$ (955.6)	$ (51.8)	$ 1.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	106.0
Net Income (Loss) Attributable to Noncontrolling Interest						0.4
Net Income (Loss) Attributable to Parent	105.6	0.0	0.0	105.6	0.0
Dividends declared	(30.1)	0.0	(30.1)	0.0	0.0	0.0
Stock-based compensation	5.2	0.0	5.2	0.0	0.0	0.0
Shares retained for employee taxes							$ (2.1)	$ 0.0	$ (2.1)	$ 0.0	$ 0.0	$ 0.0
Stock issued under stock compensation plans	7.3	0.0	7.3	0.0	0.0	0.0
Stock repurchased under buyback program	(30.0)	0.0	(30.0)	0.0	0.0	0.0
Other Comprehensive Income (Loss), Net of Tax	19.0	0.0	0.0	0.0	19.0	0.0
Balance at Sep. 30, 2018	564.8	1.6	1,444.5	(850.0)	(32.8)	1.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	64.5
Net Income (Loss) Attributable to Noncontrolling Interest						0.7
Net Income (Loss) Attributable to Parent	63.8	0.0	0.0	63.8	0.0
Dividends declared	(32.0)	0.0	(32.0)	0.0	0.0	0.0
Stock-based compensation	4.3	0.0	4.3	0.0	0.0	0.0
Shares retained for employee taxes							(1.3)	0.0	$ (1.3)	0.0	0.0	0.0
Stock issued under stock compensation plans	5.2	0.0	5.2	0.0	0.0	0.0
Stock repurchased under buyback program	(10.0)	0.0	(10.0)	0.0	0.0	0.0
Other Comprehensive Income (Loss), Net of Tax	(3.2)	0.0	0.0	0.0	(3.2)	0.0
Balance at Sep. 30, 2019	592.3	1.6	1,410.7	(786.2)	(36.0)	2.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	72.0
Net Income (Loss) Attributable to Noncontrolling Interest						0.0
Net Income (Loss) Attributable to Parent	72.0	0.0	0.0		0.0
Dividends declared	(33.1)	0.0	(33.1)	0.0	0.0	0.0
Stock-based compensation	5.3	0.0	5.3	0.0	0.0	0.0
Shares retained for employee taxes							$ (0.9)	$ 0.0		$ 0.0	$ 0.0	$ 0.0
Stock issued under stock compensation plans	3.5	0.0	3.5	0.0	0.0	0.0
Stock repurchased under buyback program	(5.0)	0.0	(5.0)	0.0	0.0	0.0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(4.7)	0.0	2.5	0.0	0.0	2.2
Other Comprehensive Income (Loss), Net of Tax	11.3	0.0	0.0	0.0	11.3	0.0
Balance at Sep. 30, 2020	$ 640.7	$ 1.6	$ 1,378.0	$ (714.2)	$ (24.7)	$ 0.0