Long-Term Debt (Details) $ in Thousands				3 Months Ended		9 Months Ended
	Nov. 02, 2020 USD ($)	May 12, 2020 USD ($)	Dec. 15, 2017 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Apr. 19, 2017 USD ($)
Bank Borrowings
Long-term Debt, excluding current maturities				$ 447,644		$ 447,644		$ 472,900
Gross interest expense including amortization of debt issuance costs				7,444	$ 9,435	23,876	$ 27,500
Capitalized interest on our unproved properties				0	0	0	200
Second Lien [Abstract]
Long-term debt, gross				453,000		453,000		479,000
New Credit Facility [Member]
Bank Borrowings
Debt Issuance Costs, Net				1,700		1,700		3,100
Second Lien Notes [Member]
Bank Borrowings
Debt Issuance Costs, Net				3,995		3,995		4,550
Long-term Debt, excluding current maturities			$ 198,000	200,000		200,000		200,000
Gross interest expense including amortization of debt issuance costs				4,600	5,200	14,100	16,000
Second Lien [Abstract]
Long-term debt, gross			200,000
Debt Instrument, Unamortized Discount			(2,000)	(1,361)		(1,361)		(1,550)
Additional notes issuable			$ 100,000
Additional interest in the event of default			0.020
Make whole premium during year 3			0.020
Make whole premium during year 4			0.010
Second Lien, Required Security Interest on Proved Reserves			85.00%
Second Lien, Required Security Interest on Oil and Gas Properties			85.00%
Discount Rate for Estimated Future Net Revenues for Proved Properties at 9%			9.00%
Second Lien, Asset Coverage Ratio, Minimum			1.25
Discount Rate for Estimated Future Net Revenues from Proved Properties			10.00%
Second Lien, Covenant, Debt to EBITDA Ratio, Minimum			4.5
Long-term debt, net				194,600		194,600
Second Lien Notes [Member] | London Interbank Offered Rate (LIBOR) [Member]
Bank Borrowings
Debt instrument escalating basis spread on base rate			0.075
Second Lien Notes [Member] | Alternative Base Interest Rate [Member]
Bank Borrowings
Debt instrument escalating basis spread on base rate			0.065
Line of Credit [Member] | New Credit Facility [Member]
Bank Borrowings
Long-term Debt, excluding current maturities				253,000		253,000		$ 279,000
Line of Credit Facility, Current Borrowing Capacity		$ 330,000
Line of Credit Facility, Maximum Borrowing Capacity		$ 600,000
Line of Credit, Letters of Credit Issuable									$ 25,000
Commitment fee basis points for the credit facility		0.50%
Line of Credit, Additional Interest Due to Payment Default		2.00%
Line of Credit, Required Security Interest on Oil and Gas Properties		85.00%
Line of Credit, Covenant, Debt to EBITDA Ratio, Minimum		4.0
Line of Credit, Covenant, Current Ratio, Minimum		1.0
Gross interest expense including amortization of debt issuance costs				$ 2,900	$ 4,200	$ 9,800	$ 11,700
Line of Credit [Member] | New Credit Facility [Member] | Subsequent Event [Member]
Bank Borrowings
Line of Credit Facility, Current Borrowing Capacity	$ 310,000
Line of Credit, Covenant, Debt to EBITDA Ratio, Minimum	3.5
Line of Credit [Member] | New Credit Facility [Member] | Minimum [Member] | Alternative Base Interest Rate [Member]
Bank Borrowings
Debt instrument escalating basis spread on base rate		0.0175
Debt Instrument Escalating Rates for Eurodollar Rate Loans		0.0275
Line of Credit [Member] | New Credit Facility [Member] | Maximum [Member] | Alternative Base Interest Rate [Member]
Bank Borrowings
Debt instrument escalating basis spread on base rate		0.0275
Debt Instrument Escalating Rates for Eurodollar Rate Loans		0.0375