Financing Schedule of Capital Units (Details) (February 2012 Offering [Member], USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
February 2012 Offering [Member]
Common Unit Offering [Abstract]
Number of Common Units (in units)	9.2
Issuance Price (in dollars per unit)	$ 27.55
Less Underwriting Discounts and Expenses	$ 8.5
Proceeds from Issuance or Sale of Equity	$ 250.2
Common Units Outstanding After Offering	184.9
Common Units Held by the Public After Offering	82.2