PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Schedule of Units) (Details)
 12 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2013
Bison Midstream
Dec. 31, 2013
Mountaineer Midstream
Dec. 31, 2013
Common
Dec. 31, 2012
Common
Dec. 31, 2011
Common
Jun. 04, 2013
Common
Bison Midstream
Dec. 31, 2013
Common
Bison Midstream
Jun. 21, 2013
Common
Mountaineer Midstream
Dec. 31, 2013
Common
Mountaineer Midstream
Dec. 31, 2012
Subordinated
Dec. 31, 2013
Subordinated
Dec. 31, 2011
Subordinated
Dec. 31, 2013
Subordinated
Bison Midstream
Dec. 31, 2013
Subordinated
Mountaineer Midstream
Dec. 31, 2012
General partner
Dec. 31, 2013
General partner
Dec. 31, 2011
General partner
Jun. 04, 2013
General partner
Bison Midstream
Dec. 31, 2013
General partner
Bison Midstream
Jun. 21, 2013
General partner
Mountaineer Midstream
Dec. 31, 2013
General partner
Mountaineer Midstream
Class of Stock [Line Items]                                                
Partners' Capital Account, Units     0         0             0         0        
Common limited partner capital units outstanding, beginning balance 24,412,427         24,412,427                                    
Subordinated limited partner capital units outstanding, begining balance 24,409,850                         24,409,850                    
General partner interests units outstanding, beginning balance 996,320                                   1,091,453          
Partner capital units outstanding, beginning balance 49,818,597.000                                              
Units issued in connection with acquisition       1,585,560.00 3,171,120.00       1,553,849 1,553,849 3,107,698 3,107,698       0 0       31,711 31,711 63,422 63,422
Common limited partner capital units outstanding, ending balance 29,079,866 24,412,427       29,079,866 24,412,427                                  
Subordinated limited partner capital units outstanding, ending balance 24,409,850 24,409,850                     24,409,850 24,409,850                    
General partner interests units outstanding, ending balance 1,091,453 996,320                               996,320 1,091,453          
Limited Partners' Capital Account, Units Issued During Period 5,892.000         5,892                                    
Partner capital units outstanding, ending balance 54,581,169 49,818,597.000                                            
Common units sold in public offering   14,380,000         14,380,000           0         0            
Partners' Capital Account, Units, Sold in Private Placement   35,436,020.00         10,029,850           24,409,850         996,320            
Partners' Capital Account, Units, Unit-based Compensation   2,577.000         2,577           0         0