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Developed and Undeveloped Acreage (Including Both Leases and Concessions) Held (Parenthetical) (Detail)
a in Thousands
Jun. 30, 2018
a
Gas and oil acreage [Line Items]  
Developed acreage, Gross 3,464
Developed acreage, Net 1,556
Undeveloped acreage, Gross 8,668
Undeveloped acreage, Net 6,027
United States [member]  
Gas and oil acreage [Line Items]  
Developed acreage, Gross 1,137
Developed acreage, Net 669
Undeveloped acreage, Gross 1,313
Undeveloped acreage, Net 1,085
United States [member] | Discontinued Operations - Onshore US Cash Generating Units [Member]  
Gas and oil acreage [Line Items]  
Developed acreage, Gross 1,039
Developed acreage, Net 633
Undeveloped acreage, Gross 210
Undeveloped acreage, Net 162