Income Taxes (Details Textuals) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Valuation Allowance [Line Items]
Loss and tax credit carryforwards - state	$ 52,366	$ 53,367
Valuation allowance	51,093	$ 51,134
Interest expense carryforward	9,000
Enhanced oil recovery credit carryforwards	57,800
Research and development credits	21,600
Alternative minimum tax credits	18,100
Unrecognized Tax Benefits	5,400
State of Louisiana [Member]
Valuation Allowance [Line Items]
Valuation allowance	41,900
State of Mississippi [Member]
Valuation Allowance [Line Items]
Valuation allowance	9,200
State of Louisiana and Mississippi [Member]
Valuation Allowance [Line Items]
Valuation allowance	$ 51,100