Consolidated Statement Of Stockholders' Equity - USD ($) $ in Millions	Total	Common stock	Accumulated deficit	Accumulated other comprehensive income (loss)	Noncontrolling Interest [Member]	Additional Paid-in Capital [Member]
Other Comprehensive Income (Loss), Net of Tax				$ 5.7
Common Stock, Dividends, Per Share, Declared	$ 0.1500
Balance at Sep. 30, 2018		$ 1.6	$ (850.0)	(32.8)	$ 1.5	$ 1,444.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared						23.7
Stock repurchased under buyback program						(10.0)
Stock-based compensation						3.4
Shares retained for employee taxes						1.4
Stock issued under stock compensation plans	$ 0.0					4.1
Net income (loss)	23.6
Net income (loss) attributable to noncontrolling interest					(0.5)
Balance at Jun. 30, 2019	567.0	1.6	(826.4)	(27.1)	2.0	1,416.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Other
Acquisition of joint venture partner's interest	$ 0.0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders					0.0
Other Comprehensive Income (Loss), Net of Tax				0.7
Common Stock, Dividends, Per Share, Declared	$ 0.0500
Balance at Mar. 31, 2019		1.6	(860.1)	(27.8)	1.9	1,433.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared						7.9
Stock repurchased under buyback program						(10.0)
Stock-based compensation						1.1
Shares retained for employee taxes						0.0
Stock issued under stock compensation plans	$ 0.0					0.5
Net income (loss)	33.7
Net income (loss) attributable to noncontrolling interest					(0.1)
Balance at Jun. 30, 2019	567.0	1.6	(826.4)	(27.1)	2.0	1,416.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Other						0.0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders					0.0
Common Stock, Value, Issued	1.6
Other Comprehensive Income (Loss), Net of Tax	$ 1.7			1.7
Common Stock, Dividends, Per Share, Declared	$ 0.1575
Balance at Sep. 30, 2019	$ 592.3	1.6	(786.2)	(36.0)	2.2	1,410.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared						24.9
Stock repurchased under buyback program						(5.0)
Stock-based compensation						3.8
Shares retained for employee taxes						0.7
Stock issued under stock compensation plans	0.0					2.6
Net income (loss)	45.3
Net income (loss) attributable to noncontrolling interest					0.0
Balance at Jun. 30, 2020	609.7	1.6	(740.9)	(34.3)	0.0	1,383.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Other						(3.2)
Acquisition of joint venture partner's interest	$ 5.2
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders					(2.2)
Other Comprehensive Income (Loss), Net of Tax				(1.2)
Common Stock, Dividends, Per Share, Declared	$ 0.0525
Balance at Mar. 31, 2020		1.6	(752.1)	(33.1)	0.0	1,390.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared						8.3
Stock repurchased under buyback program						0.0
Stock-based compensation						1.1
Shares retained for employee taxes						0.0
Stock issued under stock compensation plans	$ 0.0					0.4
Net income (loss)	11.2
Net income (loss) attributable to noncontrolling interest					0.0
Balance at Jun. 30, 2020	609.7	$ 1.6	$ (740.9)	$ (34.3)	0.0	1,383.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Other						$ 0.0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders					$ 0.0
Common Stock, Value, Issued	$ 1.6