Quarterly Financial Data (Unaudited) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended														12 Months Ended
	Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011	Dec. 31, 2010		Sep. 30, 2012	Sep. 30, 2011		Sep. 30, 2010
Quarterly Financial Data [Abstract]
Revenues	$ 47.5	[1]	$ 48.6	[1]	$ 46.9	$ 46.8	[2]	$ 43.7	[1]	$ 42.0	[1]	$ 38.6	$ 38.9	[2]	$ 189.8	$ 163.2	[3]	$ 146.9	[3]
Operating Income	14.8	[1]	18.7	[1]	16.4	17.6	[2]	13.8	[1]	15.5	[1]	12.3	11.9	[2]	67.5	53.5	[3]	42.4	[3]
Net income	13.7	[1]	18.0	[1]	16.4	17.6	[2]	13.8	[1]	15.5	[1]	12.3	11.9	[2]	65.7	53.5	[3]	43.2	[3]
Net income available to partners	$ 13.7	[1]	$ 16.4	[1]	$ 13.4	$ 1.5	[2]								$ 65.7	$ 53.5	[3]	$ 42.4	[3]
Net income per limited partner unit, Basic	0.17	[1]	0.21	[1]	0.18	0.02	[2]
Net income per limited partner unit: Diluted	0.17	[1]	0.21	[1]	0.18	0.02	[2]

[1] The fiscal 2011 period was retrospectively adjusted as described in Note 1.

[2] The fiscal 2012 and 2011 periods were retrospectively adjusted as described in Note 1.

[3] Retrospectively adjusted as described in Note 1.