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Subsequent Event (Details) - USD ($)
$ in Thousands
3 Months Ended
Jun. 30, 2017
Mar. 31, 2017
Subsequent Event [Line Items]    
Proceeds from Sale of Property Held-for-sale   $ 402,799
Knox and Coalfield [Member]    
Subsequent Event [Line Items]    
Proceeds from Sale of Property Held-for-sale $ 18,944  
Gain (Loss) on Sale of Properties 500  
Utica-Point Pleasant Shale [Member]    
Subsequent Event [Line Items]    
Proceeds from Sale of Property Held-for-sale 76,696  
Gain (Loss) on Sale of Properties $ 72,000