Quarterly report pursuant to Section 13 or 15(d)

Recent Transactions (Rockpoint Transaction) (Narrative) (Details)

v3.7.0.1
Recent Transactions (Rockpoint Transaction) (Narrative) (Details) - Investment Agreement [Member] - Rockpoint [Member] - USD ($)
$ in Millions
 3 Months Ended
Mar. 10, 2017
Feb. 27, 2017
Mar. 31, 2017
Preferred Units [Line Items]      
Incremental closing payments, Limited Partnership interest $ 150    
Minimum [Member]      
Preferred Units [Line Items]      
Incremental closing payments, Limited Partnership interest     $ 10
Maximum [Member]      
Preferred Units [Line Items]      
Contributed amount to obtain equity units   $ 300