Commitments and Contingencies (Commitments) (Details Textuals 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Anthropogenic CO2 Contracts [Member]
Long-term Purchase Commitment [Line Items]
Term of long-term purchase commitments (years)	20 years
Oil price assumption for obligation estimate ($/Bbl)	90
Anthropogenic CO2 Contracts [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Aggregate purchase obligation of CO2	$ 170
Anthropogenic CO2 Contracts [Member] | Minimum [Member]
Long-term Purchase Commitment [Line Items]
Aggregate purchase obligation of CO2	100
Volumetric production payments [Member]
Long-term Purchase Commitment [Line Items]
Term of long-term supply arrangement (years)	15 years
Significant supply commitment yearly maximum volume required (MMcf/d)	119
Volumetric production payments [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Significant supply commitment remaining volume committed (MMcf)	367,000
Riley Ridge [Member] | Helium Supply Arrangement [Member]
Long-term Purchase Commitment [Line Items]
Term of long-term supply arrangement (years)	20 years
Maximum annual payment in event of shortfall	8.0
Maximum payment in event of shortfall	$ 46.0