Discontinued Operations (Additional Information) (Detail) $ in Thousands		3 Months Ended	9 Months Ended
	Sep. 22, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) a well
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of proved property				$ (13,618)
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				$ 80,084
Reimbursement of capital costs related to sale of in progress wells				3,269
Loss related to write-off of allocated goodwill				$ 7,244
Wyoming
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss contingency accrual, decrease			$ (1,043)
Environmental liabilities		$ 1,155
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		$ 1,100
Discontinued Operations, Disposed of by Sale | Forestar Petroleum Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale of stock, consideration received on transaction	$ 100