Debt (Property and Equipment, New Credit Facility) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Sep. 27, 2019	Aug. 31, 2019	Mar. 31, 2019	Dec. 31, 2013
Line of Credit Facility [Line Items]
Financing lease obligations	$ 1,653,000
Borrowing base amount	750,000,000		$ 30,000,000		$ 4,000,000
Initial borrowing base amount	325,000,000		$ 325,000,000		$ 325,000,000
Letters of credit outstanding unused portion	$ 195,000,000
Number of days to make election to eliminate borrowings in excess of borrowing base as the result of a redetermination	10 days
Low
Line of Credit Facility [Line Items]
Commitment fee on unused portion of the borrowing base	0.375%
High
Line of Credit Facility [Line Items]
Commitment fee on unused portion of the borrowing base	0.50%
Credit facility | Election One
Line of Credit Facility [Line Items]
Number of days to eliminate borrowings in excess of borrowing base as the result of a redetermination	45 days
Credit facility | Election Two
Line of Credit Facility [Line Items]
Number of days to eliminate borrowings in excess of borrowing base as the result of a redetermination	30 days
Equal monthly installment period to eliminate borrowings in excess of borrowing base as the result of redetermination	6 months
Credit facility | Election Three
Line of Credit Facility [Line Items]
Number of days to eliminate borrowings in excess of borrowing base as the result of a redetermination	45 days
Credit facility | Alternate Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Credit facility | Alternate Base Rate | Low
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Credit facility | Alternate Base Rate | High
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Credit facility | Adjusted Libo Rate
Line of Credit Facility [Line Items]
One month interest period	1 month
Two month interest period	2 months
Three month interest period	3 months
Six month interest period	6 months
Weighted average interest rate	4.03%
Credit facility | Adjusted Libo Rate | Low
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Credit facility | Adjusted Libo Rate | High
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.00%
Letter of Credit
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.125%
CO2 Compressor
Line of Credit Facility [Line Items]
Financing lease obligations		$ 9,832,000		$ 9,832,000		$ 24,500,000
Mortgages
Line of Credit Facility [Line Items]
Time of repayment				$ 8,176,000