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Segment Information and Major Customers - Segment Information by Major Customers (Detail) - Sales [Member] - Customer Concentration Risk [Member]
12 Months Ended
Dec. 31, 2017
Oil Purchasers [Member] | Apache Corporation [Member]  
Revenue, Major Customer [Line Items]  
Revenue by major customers 28.00%
Oil Purchasers [Member] | Plains All American Inc., Oil Purchasers [Member]  
Revenue, Major Customer [Line Items]  
Revenue by major customers 23.00%
Oil Purchasers [Member] | Sunoco, Inc. [Member]  
Revenue, Major Customer [Line Items]  
Revenue by major customers 16.00%
Oil Purchasers [Member] | Shell Trading Company [Member]  
Revenue, Major Customer [Line Items]  
Revenue by major customers 10.00%
Gas Purchasers [Member] | Apache Corporation [Member]  
Revenue, Major Customer [Line Items]  
Revenue by major customers 12.00%
Gas Purchasers [Member] | Targa Pipeline Mid-Continent [Member]  
Revenue, Major Customer [Line Items]  
Revenue by major customers 25.00%