Note 4 - Debt (Details Textual) $ / shares in Units, $ in Thousands, shares in Millions					3 Months Ended
	May 29, 2019 USD ($)	May 14, 2019 USD ($) $ / shares	Oct. 17, 2017 USD ($)	Oct. 12, 2016 USD ($) $ / shares shares	Mar. 31, 2019 USD ($)		Mar. 31, 2018 USD ($)	Dec. 31, 2017	Dec. 31, 2018 USD ($)
Debt Instrument, Face Amount					$ 87,493				$ 80,691
Long-term Debt, Gross					84,969				76,820	[1]
Costless Warrants Associated with the Convertible Second Lien Notes [Member]
Warrants and Rights Outstanding, Term				10 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares				2.5
Convertible Second Lien Notes [Member]
Long-term Debt Gross Paid in Kind Interest					15,500				13,700
Debt Instrument, Unamortized Discount, Total				$ 11,000	2,500				3,900
Amortization of Debt Discount (Premium)					1,300		$ 900
Paid-in-Kind Interest					1,800		$ 1,600
Debt Instrument, Covenant Compliance Debt to EBITDAX				1.75
Debt Instrument, Covenant, Compliance Total Proved Asset Coverage Ratio								1.5
Debt Instrument, Face Amount				$ 40,000	55,493	[1]			53,691	[1]
Debt Instrument, Interest Rate, Stated Percentage				13.50%
Debt Instrument, Convertible, Conversion Price | $ / shares				$ 21.33
Debt Instrument, Convertible, Number of Equity Instruments				1,900,000
Long-term Debt, Gross				$ 29,000	52,969	[1]			49,820	[1]
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature				$ 11,000
Convertible Second Lien Notes [Member] | Forecast [Member]
Debt Conversion, Original Debt, Amount	$ 56,700
Convertible Second Lien Notes [Member] | Minimum [Member]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage				25.00%
The 2017 Senior Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity					250,000
Line of Credit Facility, Current Borrowing Capacity					$ 75,000
Line of Credit Facility, Commitment Fee Percentage			0.50%
Line of Credit Facility, Interest Rate at Period End, Default Rate			2.00%
Debt Instrument, Covenant Compliance Debt to EBITDAX			4
Debt Instrument, Covenant, Current Ratio			1		1
Debt Instrument, Covenant Compliance Unrestricted Cash, Maximum			$ 10,000
Debt Instrument, Covenant, Compliance Total Proved Asset Coverage Ratio			1.5
Long-term Line of Credit, Total					$ 32,000
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net, Total					500
Debt Instrument, Face Amount					32,000				27,000
Long-term Debt, Gross					32,000				$ 27,000
The 2017 Senior Credit Facility [Member] | Line of Credit Draw Limit [Member]
Line of Credit Facility, Current Borrowing Capacity					$ 50,000
The 2017 Senior Credit Facility [Member] | Minimum [Member]
Debt Instrument, Interest Rate, Effective Percentage					5.74%
The 2017 Senior Credit Facility [Member] | Minimum [Member] | Base Rate [Member]
Debt Instrument, Basis Spread on Variable Rate			1.75%
The 2017 Senior Credit Facility [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate			2.75%
The 2017 Senior Credit Facility [Member] | Maximum [Member]
Debt Instrument, Interest Rate, Effective Percentage					7.50%
The 2017 Senior Credit Facility [Member] | Maximum [Member] | Base Rate [Member]
Debt Instrument, Basis Spread on Variable Rate			2.75%
The 2017 Senior Credit Facility [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate			3.75%
The 2017 Senior Credit Facility [Member] | Line of Credit Draw Limit [Member]
Line of Credit Facility, Elective Draw Capacity					$ 50,000
The 2017 Senior Credit Facility [Member] | Letter of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity			$ 10,000
The 2019 Senior Credit Facility [Member] | Subsequent Event [Member]
Line of Credit Facility, Maximum Borrowing Capacity		$ 500,000
Line of Credit Facility, Current Borrowing Capacity		$ 115,000
Line of Credit Facility, Interest Rate at Period End, Default Rate		2.00%
Debt Instrument, Covenant Compliance Debt to EBITDAX		4
Debt Instrument, Covenant, Current Ratio		1
Debt Instrument, Covenant Compliance Unrestricted Cash, Maximum		$ 10,000
Debt Instrument, Covenant, Compliance Total Proved Asset Coverage Ratio		1.5
The 2019 Senior Credit Facility [Member] | Minimum [Member] | Subsequent Event [Member]
Line of Credit Facility, Commitment Fee Percentage		0.375%
The 2019 Senior Credit Facility [Member] | Minimum [Member] | Base Rate [Member] | Subsequent Event [Member]
Debt Instrument, Basis Spread on Variable Rate		1.50%
The 2019 Senior Credit Facility [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member] | Subsequent Event [Member]
Debt Instrument, Basis Spread on Variable Rate		2.50%
The 2019 Senior Credit Facility [Member] | Maximum [Member] | Subsequent Event [Member]
Line of Credit Facility, Commitment Fee Percentage		0.50%
The 2019 Senior Credit Facility [Member] | Maximum [Member] | Base Rate [Member] | Subsequent Event [Member]
Debt Instrument, Basis Spread on Variable Rate		2.50%
The 2019 Senior Credit Facility [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member] | Subsequent Event [Member]
Debt Instrument, Basis Spread on Variable Rate		3.50%
New Convertible Second Lien Notes, New 2L Notes [Member] | Subsequent Event [Member]
Debt Instrument, Face Amount		$ 12,000
Debt Instrument, Interest Rate, Stated Percentage		13.50%
Debt Instrument, Convertible, Conversion Price | $ / shares		$ 21.33

[1] The debt discount is being amortized using the effective interest rate method based upon a maturity date of August 30, 2019. The principal includes $15.5 million and $13.7 million of paid in-kind interest as of March 31, 2019 and December 31, 2018, respectively. The carrying value includes $2.5 million and $3.9 million of unamortized debt discount as of March 31, 2019 and December 31, 2018, respectively.