Long-Term Debt - Additional Information (Detail)		1 Months Ended	9 Months Ended
	Jul. 31, 2017 USD ($)	Aug. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Citizen 2017 Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, expiration period	2 years
Line of credit facility, maximum borrowing capacity	$ 500,000,000.0
Line of credit facility, current borrowing capacity	$ 82,500,000
Outstanding borrowing, amount repaid		$ 20,300,000
2017 Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity				$ 750,000,000
Line of credit facility, current borrowing capacity			$ 675,000,000.0	$ 200,000,000.0
Line of credit facility, outstanding borrowings			$ 394,600,000
Percentage of projected production hedged			80.00%
Borrowings outstanding threshold percentage			50.00%
Minimum future production hedge percentage			50.00%
Debt to EBITDAX Ratio			4.00
Current assets to current liabilities			1.00
2017 Credit Facility | Level I
Line of Credit Facility [Line Items]
Commitment Fee			0.375%
2017 Credit Facility | Level II
Line of Credit Facility [Line Items]
Commitment Fee			0.375%
2017 Credit Facility | LIBOR Margin
Line of Credit Facility [Line Items]
Reduction of applicable margin rate			0.25%
2017 Credit Facility | Applicable Margin
Line of Credit Facility [Line Items]
Reduction of applicable margin rate			0.25%
2017 Credit Facility | Letter of credit
Line of Credit Facility [Line Items]
Line of credit facility, outstanding borrowings			$ 0
Amended 2017 Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity			$ 500,000,000