Commitments and Contingencies Commitments and Contingencies (Details Textuals 3)	12 Months Ended
	Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Estimated Litigation Liability	$ 46,000,000
Material tax assessments	0
Denbury [Member]
Loss Contingencies [Line Items]
Termination fee in event of contract termination	45,000,000
Penn Virginia
Loss Contingencies [Line Items]
Termination fee in event of contract termination	45,000,000
Liquidated damages through the contract year ending July 31, 2017
Loss Contingencies [Line Items]
Estimated Litigation Liability	31,800,000
Other costs associated with the settlement
Loss Contingencies [Line Items]
Estimated Litigation Liability	3,400,000
Liquidated damages for contract years ending July 31, 2018 and July 31, 2019
Loss Contingencies [Line Items]
Estimated Litigation Liability	$ 14,200,000