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Discontinued Operations (Additional Information) (Detail)
$ in Thousands
 12 Months Ended
Dec. 31, 2016
USD ($)
a
well
Dec. 31, 2015
USD ($)
a
well
Dec. 31, 2014
USD ($)
a
well
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
(Loss) gain on disposition of proved property $ (13,664) $ (706) $ 8,526
Net mineral acres leased from others sold | a 199,263    
Gross producing oil and gas wells sold | well 379    
Net producing oil and gas wells sold | well 95    
Proceeds from sale of oil and gas property and equipment $ 80,374 17,800 17,660
Reimbursement of capital costs related to sale of in progress wells 3,269    
Non-cash impairment charges 60,939 $ 108,184 $ 15,934
Pending Litigation | Huffman vs. Forestar Petroleum Corporation      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Accrual for damages 2,990    
Wyoming      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Environmental liability 1,155    
Transaction      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Gas and oil area, undeveloped, net | a   109,000 650
Productive oil wells, number of wells, gross | well   39 124
Productive oil wells, number of wells, net | well   7 18
Cost of Sales      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Non-cash impairment charges $ 612 $ 163,029 $ 32,665