Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) - Narrative (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) MMBTU MBoe $ / MMBTU $ / bbl	Dec. 31, 2017 USD ($) MBoe Well $ / MMBTU $ / bbl	Dec. 31, 2016 USD ($) MBoe
Reserve Quantities [Line Items]
Additions to oil and gas properties | $	$ 226,628,000	$ 638,842,000
Capitalized exploratory well costs | $	$ 0	$ 0
Natural gas liquids prices used to value reserves | $ / bbl	28.81	22.59
Proved extensions and discoveries	16,209	30,763
Sales of minerals in place	(6,596)	(2,976)
Purchases of minerals in place	6,810	45,911
Number of wells acquired | Well		63
Revision to previous estimates	(6,075)	2,901
Revisions	(5,838)	4,832
Improved proved developed reserves	300	1,931
Removal of proved undeveloped reserves		2,011
Conversion period of proved undeveloped reserves into proved developed producing reserves			5 years
Estimated capital expenditures of proved undeveloped reserves | $	$ 51,900,000		$ 6,900,000
Estimated conversion of proved undeveloped reserves into proved developed producing reserves	4,300	622
Capital expenditures of proved undeveloped reserves | $	$ 55,400,000	$ 8,500,000
Sales of minerals in place	(4,702)	(391)
Modified conversion of proved undeveloped reserves into proved developed producing reserves	4.4
Conversion of proved undeveloped reserves into proved developed producing reserves	4,419	2,756	732
Extensions and discoveries	13,734	27,977
Non-cancelable Agreement
Reserve Quantities [Line Items]
Holding pipeline capacity | MMBTU	10,000
Eagle Ford
Reserve Quantities [Line Items]
Proved undeveloped reserves excepted volume to be developed		443
Bold Transaction
Reserve Quantities [Line Items]
Reduction of proved undeveloped reserves		2,378
Capital expenditures of proved undeveloped reserves | $		$ 63,400,000
Conversion of proved undeveloped reserves into proved developed producing reserves		2,134
Added to proved undeveloped reserves		37,327
Midland Basin
Reserve Quantities [Line Items]
Proved extensions and discoveries	16,200
Purchases of minerals in place	4,700
Sales of minerals in place	4,700	391
Proved undeveloped reserves sales of minerals in place, disposed of during period	3,700
Extensions and discoveries	13,700	27,977
Midland Basin | Bold Transaction
Reserve Quantities [Line Items]
Purchases of minerals in place	6,800
Eagle Ford
Reserve Quantities [Line Items]
Sales of minerals in place	(1,900)
Sales of minerals in place	1,000
Williston Basin
Reserve Quantities [Line Items]
Sales of minerals in place	(6,600)	(2,976)
Henry Hub Spot Price
Reserve Quantities [Line Items]
Unweighted average of first of the month prices of natural gas | $ / MMBTU	3.10	2.98
West Texas Intermediate Spot Price
Reserve Quantities [Line Items]
Unweighted average of first of the month prices of oil | $ / bbl	65.56	51.34
New Wells
Reserve Quantities [Line Items]
Additions to oil and gas properties | $	$ 300,000	$ 100,000
Operated Eagle Ford and Non-operated Bakken Properties
Reserve Quantities [Line Items]
Proved extensions and discoveries		30,763
Non-operated Midland Basin Properties | Lynden Arrangement
Reserve Quantities [Line Items]
Purchases of minerals in place		45,911