Commitments and Contingencies (Commitments) (Details Textuals 1) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) MMcf / d $ / Barrel MMcf
Industrial-source CO2 [Member]
Long-term Purchase Commitment [Line Items]
Term of Long Term Purchase Commitments	15 years
Oil price assumption for obligation estimate ($/Bbl) | $ / Barrel	60
Industrial-source CO2 [Member] | Minimum
Long-term Purchase Commitment [Line Items]
Aggregate purchase obligation of CO2	$ 14.0
Industrial-source CO2 [Member] | Maximum
Long-term Purchase Commitment [Line Items]
Aggregate purchase obligation of CO2	$ 33.0
CO2 Volumetric Production Payments and Industrial CO2 Customers [Member]
Long-term Purchase Commitment [Line Items]
Significant supply commitment remaining volume committed (MMcf) | MMcf	633,152
Significant supply commitment yearly maximum volume required (MMcf/d) | MMcf / d	176
Term of Long Term Supply Arrangement	15 years
Helium Supply Arrangement [Member]
Long-term Purchase Commitment [Line Items]
Term of Long Term Supply Arrangement	20 years
Maximum annual payment in event of shortfall	$ 8.0
Maximum payment in event of shortfall	$ 46.0