Certain Balance Sheet Information Certain Balance Sheet Information - Components of Property Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 816.9	$ 630.1	$ 1,068.7	$ 816.9	$ 630.1
Less: accumulated depreciation	152.9		200.8	152.9
Property, plant and equipment, net	664.0		867.9	664.0
Depreciation			47.8	40.8	38.5
Depletion	0.2	0.2	0.2
Plant Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	173.4		225.3	173.4
Salt Deposits [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	41.6		41.6	41.6
Land and Building [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	358.0		393.3	358.0
Vehicles [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	2.5		3.0	2.5
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	169.6		331.4	169.6
Base Gas [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	71.1		73.1	71.1
Furniture And Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 0.7		$ 1.0	$ 0.7