Long-Term Debt (Details) $ in Thousands				12 Months Ended
	Nov. 02, 2020 USD ($)	May 12, 2020 USD ($)	Dec. 15, 2017 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Apr. 19, 2017 USD ($)
Bank Borrowings
Long-Term Debt, excluding current maturities				$ 424,905	$ 472,900
Interest expense including commitment fees and amortization of debt issuance costs relating to the credit facility				31,228	36,561
Second Lien
Long-term Debt, Gross				$ 430,000	479,000
Discount Rate for Estimated Future Net Revenues from Proved Properties				10.00%
Line of Credit [Member]
Bank Borrowings
Capitalized interest on our unproved properties				$ 0	200
New Credit Facility [Member]
Bank Borrowings
Debt Issuance Costs, Net				(1,400)	(3,100)
New Credit Facility [Member] | Line of Credit [Member]
Bank Borrowings
Long-Term Debt, excluding current maturities				230,000	279,000
Line of Credit, current borrowing base	$ 310,000	$ 330,000		310,000
Line of Credit Facility, Maximum Borrowing Capacity		$ 600,000
Line of Credit, Letters of Credit Issuable						$ 25,000
Line of Credit Facility, Commitment Fee Percentage		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	3.5	4.0
Line of Credit, Covenant, Current Ratio, Minimum		1.0
Interest expense including commitment fees and amortization of debt issuance costs relating to the credit facility				12,600	15,700
Commitment fees included in interest expense, net				400	700
New Credit Facility [Member] | Line of Credit [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
New Credit Facility [Member] | Line of Credit [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
Second Lien Notes [Member]
Bank Borrowings
Debt Issuance Costs, Net				(3,800)	(4,550)
Long-Term Debt, excluding current maturities			$ 198,000	200,000	200,000
Interest expense including commitment fees and amortization of debt issuance costs relating to the credit facility				18,600	21,100
Second Lien
Long-term Debt, Gross			200,000
Debt Instrument, Unamortized Discount			(2,000)	(1,295)	$ (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				$ 194,900
Second Lien Notes [Member] | Alternative Base Interest Rate [Member]
Bank Borrowings
Debt Instrument escalating basis spread on base rate			0.065
Second Lien Notes [Member] | London Interbank Offered Rate (LIBOR) [Member]
Bank Borrowings
Debt Instrument escalating basis spread on base rate			0.075