Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Goodwill acquired on acquisition	$ 0	$ 37,900,000
Non-cash impairment charges	47,172,000	60,939,000	$ 108,184,000
Unproved leasehold interests
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Goodwill acquired on acquisition	0	$ 37,900,000
Water Resources Company | Groundwater Leases
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Non-cash impairment charges	1,233,000
Texas | Water Resources Company
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Non-cash impairment charges	3,874,000
The Mineral Companies | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Goodwill, impairment loss	37,900,000
Non-cash impairment charges	$ 37,900,000