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, 2014	$ 351.6	$ 1.6	$ 1,582.8	$ (1,173.7)	$ (60.7)	$ 1.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	30.8
Net Income (Loss) Attributable to Noncontrolling Interest						(0.1)
Net Income (Loss) Attributable to Parent	30.9	0.0	0.0	30.9	0.0
Dividends declared	(12.0)	0.0	(12.0)	0.0	0.0	0.0
Stock-based compensation	4.9	0.0	4.9	0.0	0.0	0.0
Excess tax benefit on stock option exercises	3.2	0.0	3.2	0.0	0.0	0.0
Shares retained for employee taxes							$ (2.4)	$ 0.0	$ (2.4)	$ 0.0	$ 0.0	$ 0.0
Stock issued under stock compensation plans	3.3	0.0	3.3	0.0	0.0	0.0
Stock repurchased under buyback program	(5.0)	0.0	5.0	0.0	0.0	0.0
Other Comprehensive Income (Loss), Net of Tax	(6.6)	0.0	0.0	0.0	(6.6)	0.0
Balance at Sep. 30, 2015	367.8	1.6	1,574.8	(1,142.8)	(67.3)	1.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	63.6
Net Income (Loss) Attributable to Noncontrolling Interest						(0.3)
Net Income (Loss) Attributable to Parent	63.9	0.0	0.0	63.9	0.0
Dividends declared	(16.1)	0.0	(16.1)	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							(3.3)	0.0	$ (3.3)	0.0	0.0	0.0
Stock issued under stock compensation plans	3.3	0.0	3.3	0.0	0.0	0.0
Other Comprehensive Income (Loss), Net of Tax	(1.0)	0.0	0.0	0.0	(1.0)	0.0
Balance at Sep. 30, 2016	419.5	1.6	1,563.9	(1,078.9)	(68.3)	1.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	123.2
Net Income (Loss) Attributable to Noncontrolling Interest						(0.1)
Net Income (Loss) Attributable to Parent	123.3	0.0	0.0		0.0
Dividends declared	(24.0)	0.0	(24.0)	0.0	0.0	0.0
Stock-based compensation	6.2	0.0	6.2	0.0	0.0	0.0
Shares retained for employee taxes							$ (2.7)	$ 0.0		$ 0.0	$ 0.0	$ 0.0
Stock issued under stock compensation plans	5.8	0.0	5.8	0.0	0.0	0.0
Stock repurchased under buyback program	(55.0)	0.0	55.0	0.0	0.0	0.0
Payments to Acquire Interest in Joint Venture	1.7
Other Comprehensive Income (Loss), Net of Tax	16.5	0.0	0.0	0.0	16.5	0.0
Balance at Sep. 30, 2017	$ 489.5	$ 1.6	$ 1,494.2	$ (955.6)	$ (51.8)	$ 1.1