Guarantor Subsidiaries - Schedule of Condensed Consolidating Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	$ 231,441	$ 121,990	$ 121,736
Cash flows from investing activities:
Additions to oil and gas properties, including acquisitions	(453,616)	(239,631)	(106,870)
Additions to furniture, fixtures and other	(853)	(926)	(1,195)
Repayment of debt associated with merger, net of cash acquired	(53,357)	0	0
Proceeds from sale of properties and other investing activities	143	101,546	24,927
Intercompany transfers		0	0
Cash flows from financing activities:
Proceeds from debt	0	275,000
Principal and redemption premium payments on debt	(469)	(322,343)	(440)
Proceeds from sale of common stock, net of offering costs	1	110,710	110,003
Intercompany transfers		0	0
Other financing activities	(4,982)	(7,721)	(1,156)
Increase (Decrease) in Cash and Cash Equivalents	(281,692)	38,625	147,005
Beginning Cash and Cash Equivalents	314,466	275,841	128,836
Ending Cash and Cash Equivalents	32,774	314,466	275,841
Reportable Legal Entities [Member] \| Parent Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities		121,480	121,109
Cash flows from investing activities:
Additions to oil and gas properties, including acquisitions		(239,631)	(106,852)
Additions to furniture, fixtures and other		(926)	(1,195)
Proceeds from sale of properties and other investing activities		99,016	24,802
Intercompany transfers		3,040	734
Cash flows from financing activities:
Proceeds from debt		275,000
Principal and redemption premium payments on debt		(322,343)	(440)
Proceeds from sale of common stock, net of offering costs		110,710	110,003
Intercompany transfers		0	0
Other financing activities		(7,721)	(1,156)
Increase (Decrease) in Cash and Cash Equivalents		38,625	147,005
Beginning Cash and Cash Equivalents	314,466	275,841	128,836
Ending Cash and Cash Equivalents		314,466	275,841
Reportable Legal Entities [Member] \| Parent Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	0
Cash flows from investing activities:
Additions to oil and gas properties, including acquisitions	0
Additions to furniture, fixtures and other	0
Repayment of debt associated with merger, net of cash acquired	0
Proceeds from sale of properties and other investing activities	0
Cash flows from financing activities:
Proceeds from debt	0
Principal and redemption premium payments on debt	0
Proceeds from sale of common stock, net of offering costs	0
Other financing activities	0
Increase (Decrease) in Cash and Cash Equivalents	0
Beginning Cash and Cash Equivalents	0
Ending Cash and Cash Equivalents	0	0
Reportable Legal Entities [Member] \| Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities		510	627
Cash flows from investing activities:
Additions to oil and gas properties, including acquisitions		0	(18)
Additions to furniture, fixtures and other		0	0
Proceeds from sale of properties and other investing activities		2,530	125
Intercompany transfers		0	0
Cash flows from financing activities:
Proceeds from debt		0
Principal and redemption premium payments on debt		0	0
Proceeds from sale of common stock, net of offering costs		0	0
Intercompany transfers		(3,040)	(734)
Other financing activities		0	0
Increase (Decrease) in Cash and Cash Equivalents		0	0
Beginning Cash and Cash Equivalents	0	0	0
Ending Cash and Cash Equivalents		0	0
Reportable Legal Entities [Member] \| Subsidiary Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	231,441
Cash flows from investing activities:
Additions to oil and gas properties, including acquisitions	(453,616)
Additions to furniture, fixtures and other	(853)
Repayment of debt associated with merger, net of cash acquired	(53,357)
Proceeds from sale of properties and other investing activities	143
Cash flows from financing activities:
Proceeds from debt	0
Principal and redemption premium payments on debt	(469)
Proceeds from sale of common stock, net of offering costs	1
Other financing activities	(4,982)
Increase (Decrease) in Cash and Cash Equivalents	(281,692)
Beginning Cash and Cash Equivalents	314,466
Ending Cash and Cash Equivalents	32,774	314,466
Intercompany Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	0	0	0
Cash flows from investing activities:
Additions to oil and gas properties, including acquisitions	0	0	0
Additions to furniture, fixtures and other	0	0	0
Repayment of debt associated with merger, net of cash acquired	0
Proceeds from sale of properties and other investing activities	0	0	0
Intercompany transfers		(3,040)	(734)
Cash flows from financing activities:
Proceeds from debt	0	0
Principal and redemption premium payments on debt	0	0	0
Proceeds from sale of common stock, net of offering costs	0	0	0
Intercompany transfers		3,040	734
Other financing activities	0	0	0
Increase (Decrease) in Cash and Cash Equivalents	0	0	0
Beginning Cash and Cash Equivalents	0	0	0
Ending Cash and Cash Equivalents	$ 0	$ 0	$ 0

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Intercompany Transfers Investing Activities

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Payment Of Debt Associated With Merger, Net Of Cash Acquired

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The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale. In addition, includes the net cash outflow (inflow) from other investing activities.

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Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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The cash outflow for exploration and development of oil and gas properties. It includes cash payments related to development of oil and gas wells drilled at previously untested geologic structures (to determine the presence of oil or gas) and wells drilled at sites where the presence of oil or gas has already been established (to extract the oil or gas).

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