Sale of Oil and Natural Gas Property Interests - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018 USD ($) a	Mar. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of assets	$ 267,000	$ 5,000
Asset Sale 400 Acres [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of assets	0
Proceeds from sale of asset	$ 3,800,000
Area of land | a	400
Asset Sale 50 Acres [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of assets	$ 300,000
Proceeds from sale of asset	$ 300,000
Area of land | a	50