Annual report pursuant to Section 13 and 15(d)

Equity Method Investments (Details)

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Equity Method Investments (Details)
$ in Thousands
12 Months Ended
Feb. 06, 2017
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Jun. 30, 2016
mi
Equity Method Investments        
Contribution to joint venture   $ 235,004 $ 75,516  
Investments in unconsolidated affiliates        
Balance at beginning of period   68,299    
Initial investment   153,770 45,044  
Additional investments   81,234 30,472  
Equity in net income of unconsolidated affiliates   20,194 485  
Distributions from unconsolidated affiliates   (20,195) (7,702)  
Balance at end of period   303,302 68,299  
Appalachia Joint venture        
Equity Method Investments        
Ownership percentage 50.00%      
Percentage of interest held by joint venture in third party fractionator in Ohio 33.33%      
Investments in unconsolidated affiliates        
Initial investment   153,770    
Additional investments   81,234    
Equity in net income of unconsolidated affiliates   9,890    
Distributions from unconsolidated affiliates   (8,720)    
Balance at end of period   $ 236,174    
Appalachia Joint venture | MarkWest        
Equity Method Investments        
Ownership percentage 50.00%      
Stonewall Gas Gathering LLC        
Equity Method Investments        
Ownership percentage   15.00%   15.00%
Number of miles | mi       67
Investments in unconsolidated affiliates        
Balance at beginning of period   $ 68,299    
Initial investment     45,044  
Additional investments     30,472  
Equity in net income of unconsolidated affiliates   10,304 485  
Distributions from unconsolidated affiliates   (11,475) (7,702)  
Balance at end of period   $ 67,128 $ 68,299