Amounts Related To Plant Closures (Schedule Of Amounts Related To Plant Closures) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2011
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 6.7	$ 0.2	$ 6.8	$ 0.4
Los Alamitos [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits	0.5		0.5
Losses on property	0.4		0.4
Other associated costs	0.2		0.2
Restructuring costs	1.1		1.1
Poteau [Member]
Restructuring Cost and Reserve [Line Items]
Losses on property	4.9		4.9
Restructuring costs	4.9		4.9
Billerica And Blue Island [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0.7	0.2	0.8	0.4
Cumulative Total [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	16.5
Cumulative Total [Member] | Los Alamitos [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits	0.5
Losses on property	0.4
Other associated costs	0.2
Restructuring costs	1.1
Cumulative Total [Member] | Poteau [Member]
Restructuring Cost and Reserve [Line Items]
Losses on property	4.9
Restructuring costs	4.9
Cumulative Total [Member] | Billerica And Blue Island [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	10.5
Total Expected To Be Incurred [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	21.8
Total Expected To Be Incurred [Member] | Los Alamitos [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits	0.5
Losses on property	0.4
Other associated costs	0.4
Restructuring costs	1.3
Total Expected To Be Incurred [Member] | Poteau [Member]
Restructuring Cost and Reserve [Line Items]
Employee termination benefits	2.3
Losses on property	4.9
Other associated costs	2.5
Restructuring costs	9.7
Total Expected To Be Incurred [Member] | Billerica And Blue Island [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 10.8