Quarterly report pursuant to Section 13 or 15(d)

Equity Method Investments (Details)

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Equity Method Investments (Details)
$ in Thousands
3 Months Ended
Feb. 06, 2017
Mar. 31, 2018
USD ($)
Mar. 31, 2017
USD ($)
Jun. 30, 2016
mi
Equity Method Investments        
Contribution to joint venture   $ 17,389 $ 159,889  
Investments in unconsolidated affiliates        
Balance at beginning of period   303,302    
Additional investments   17,389    
Equity in net income of unconsolidated affiliates   7,862 $ 2,231  
Distributions from unconsolidated affiliates   (7,085)    
Balance at end of period   321,468    
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        
Balance at beginning of period   236,174    
Additional investments   17,389    
Equity in net income of unconsolidated affiliates   5,124    
Distributions from unconsolidated affiliates   (6,215)    
Balance at end of period   $ 252,472    
Appalachia Joint venture | MarkWest        
Equity Method Investments        
Ownership percentage 50.00% 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   $ 67,128    
Equity in net income of unconsolidated affiliates   2,738    
Distributions from unconsolidated affiliates   (870)    
Balance at end of period   $ 68,996