Public Offering of units and Certain Provisions of the Partnership Agreement (Details Textuals) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Public Placement [Member] | May 15, 2012 [Member]
Subsidiary, Sale of Stock [Line Items]
Common units issuance date	May 15, 2012
Limited Partners Unit Price Per Unit	$ 16.28
General Partners' Contributed Capital	$ 3.4
Partners' Capital Account, Units, Sold in Public Offering	10,120,000
Proceeds from Issuance of Common Stock	158.0
Public Placement [Member] | January 14, 2013 [Member]
Subsidiary, Sale of Stock [Line Items]
Common units issuance date	Jan. 14, 2013
Limited Partners Unit Price Per Unit	$ 15.15
Partners' Capital Account, Units, Sold in Public Offering	8,625,000
Proceeds from Issuance of Common Stock	125.5
Private Placement [Member] | September 14, 2012 [Member]
Subsidiary, Sale of Stock [Line Items]
Common units issuance date	Sep. 14, 2012
Limited Partners Unit Price Per Unit	$ 13.25
Partners' Capital Account, Units, Sold in Private Placement	5,660,378
Proceeds from Issuance of Private Placement	74.8
Private Placement [Member] | January 14, 2013 [Member]
Subsidiary, Sale of Stock [Line Items]
Limited Partners Unit Price Per Unit	$ 14.55
Partners' Capital Account, Units, Sold in Private Placement	2,700,000
Proceeds from Issuance of Private Placement	$ 39.3