Annual report pursuant to Section 13 and 15(d)

Cash Distributions and Net Income (Loss) per Common Unit - Schedule of Partner Distributions Made (Details)

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Cash Distributions and Net Income (Loss) per Common Unit - Schedule of Partner Distributions Made (Details) (USD $)
0 Months Ended 1 Months Ended 3 Months Ended 12 Months Ended
Mar. 26, 2007
Sep. 30, 2012
May 31, 2012
Sep. 30, 2011
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, 2010
Jun. 30, 2010
Mar. 31, 2010
Dec. 31, 2009
Dec. 31, 2012
Dec. 31, 2011
Distribution Made to Member or Limited Partner [Line Items]                                    
Number of days after quarter end distribution is paid                                 $ 45  
Date paid         Nov. 14, 2012 Aug. 13, 2012 May 14, 2012 Feb. 12, 2012 Nov. 14, 2011 Aug. 12, 2011 May 13, 2011 Feb. 11, 2011 Nov. 12, 2010 Aug. 13, 2010 May 14, 2010 Feb. 12, 2010    
Total distribution                                 333,453,000 313,619,000
Partner units issued and sold     133,300,000                              
Partner units issued and sold, unit price ($US$ per unit) $ 21.00 $ 15.00                                
Proceeds from sale of partnership units   194,000,000 2,000,000,000 60,000,000                         11,100,000 9,000,000
Common Units
                                   
Distribution Made to Member or Limited Partner [Line Items]                                    
Distribution per unit         0.425 0.425 0.425 0.425 0.425 0.425 0.425 0.425 0.425 0.425 0.425 0.425    
Total distribution         16,783,000 13,383,000 13,323,000 13,176,000 13,176,000 11,446,000 11,335,000 11,229,000 11,227,000 11,227,000 11,227,000 11,227,000    
Partner units issued and sold, unit price ($US$ per unit)   $ 25.07                                
Class B Unit [Member]
                                   
Distribution Made to Member or Limited Partner [Line Items]                                    
Total distribution         0 0 0 0 0 0 0 0 0 0 0 0    
Subordinated Units
                                   
Distribution Made to Member or Limited Partner [Line Items]                                    
Distribution per unit         0.000 0.000     0.000 0.000 0.000 0.000 0.000 0.000 0.425 0.425    
Total distribution         0 0     0 0 0 0 0 0 57,538,000 57,538,000    
General Partner [Member]
                                   
Distribution Made to Member or Limited Partner [Line Items]                                    
Total distribution         342,000 273,000 272,000 269,000 269,000 234,000 231,000 229,000 229,000 229,000 1,403,000 1,403,000