Discontinued Operations (Additional Information) (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($) a well	Jun. 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		$ (3,596)	$ (10,977)
Net mineral acres leased from others sold | a		8,100	190,960
Gross producing oil and gas wells sold | well		175	185
Net producing oil and gas wells sold | well		16	66
Proceeds from sale of oil and gas property and equipment		$ 46,986	$ 32,227
Reimbursement of capital costs related to sale of in progress wells		$ 3,269	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)