Long-Term Debt (Details) $ in Thousands				3 Months Ended		9 Months Ended
	Nov. 06, 2018 USD ($)	Dec. 15, 2017 USD ($)	Apr. 19, 2017 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Oct. 17, 2019 USD ($)	Dec. 31, 2018 USD ($)
Bank Borrowings
Long-term Debt, excluding current maturities				$ 475,663		$ 475,663			$ 387,988
Gross interest expense including amortization of debt issuance costs				9,435	$ 7,212	27,500	$ 19,686
Capitalized interest on our unproved properties				0	200	200	900
Second Lien [Abstract]
Long-term debt, gross				482,000		482,000			395,000
New Credit Facility [Member]
Bank Borrowings
Debt Issuance Costs, Net				3,500		3,500			4,500
Second Lien Notes [Member]
Bank Borrowings
Debt Issuance Costs, Net				4,727		4,727			5,230
Long-term Debt, excluding current maturities		$ 198,000		200,000		200,000			200,000
Debt instrument escalating basis spread on base rate		50
Gross interest expense including amortization of debt issuance costs				5,200	5,300	16,000	15,300
Second Lien [Abstract]
Long-term debt, gross		$ 200,000
Debt Instrument, Unamortized Discount		(2,000)		(1,610)		(1,610)			(1,782)
Additional notes issuable		$ 100,000
Additional interest in the event of default		0.020
Make whole premium during years 1 and 2		0.02
Make whole premium during year 3		0.02
Make whole premium during year 4		0.01
Second Lien, Required Security Interest on Proved Reserves		85.00%
Second Lien, Required Security Interest on Oil and Gas Properties		85.00%
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				193,700		193,700
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
Line of Credit [Member] | New Credit Facility [Member]
Bank Borrowings
Long-term Debt, excluding current maturities				282,000		282,000			$ 195,000
Line of Credit Facility, Current Borrowing Capacity	$ 410,000
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				$ 4,200	$ 2,100	$ 11,700	$ 5,100
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	0.0100
Debt Instrument Escalating Rates for Eurodollar Rate Loans	0.0200
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	0.0200
Debt Instrument Escalating Rates for Eurodollar Rate Loans	0.0300
Subsequent Event [Member] | Line of Credit [Member] | New Credit Facility [Member]
Bank Borrowings
Line of Credit Facility, Current Borrowing Capacity								$ 400,000