Segments Segments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011		Sep. 30, 2010
Segment Reporting Information [Line Items]
Firm storage revenues	$ 94.5	$ 90.4		$ 81.0
Salt revenues	52.0	52.3	[1]	52.2	[1]
Transportation revenues	28.4	14.0	[1]	12.1	[1]
Hub services revenue	14.9	6.5	[1]	1.6	[1]
Gross profit (excluding depreciation and amortization)	148.4	116.8		104.9
Identifiable assets	24.9	21.2		18.0
Goodwill	96.5	96.5		96.5
Property, plant and equipment	1,068.7	816.9		630.1
Total assets	1,027.9	813.7		667.5
Expenditures for property, plant and equipment	251.9	120.6		55.7
Storage And Transportation Operations
Segment Reporting Information [Line Items]
Firm storage revenues	94.5	90.4		81.0
Salt revenues	0	0		0
Transportation revenues	28.4	14.0		12.1
Hub services revenue	14.9	6.5		1.6
Gross profit (excluding depreciation and amortization)	126.7	95.1		82.7
Identifiable assets	14.0	10.8		8.5
Goodwill	90.2	90.2		90.2
Property, plant and equipment	953.3	707.4		529.3
Total assets	925.9	702.4		559.6
Expenditures for property, plant and equipment	245.9	112.0		44.1
Salt Operations
Segment Reporting Information [Line Items]
Firm storage revenues	0	0		0
Salt revenues	52.0	52.3		52.2
Transportation revenues	0	0		0
Hub services revenue	0	0		0
Gross profit (excluding depreciation and amortization)	21.7	21.7		22.2
Identifiable assets	10.9	10.4		9.5
Goodwill	6.3	6.3		6.3
Property, plant and equipment	115.4	109.5		100.8
Total assets	102.0	111.3		107.9
Expenditures for property, plant and equipment	$ 6.0	$ 8.6		$ 11.6

[1] Retrospectively adjusted as described in Note 1.