Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details Textual)	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) Purchasers	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) $ / bbl	Dec. 31, 2020 USD ($) $ / MMBTU	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) Purchasers	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) $ / bbl	Dec. 31, 2019 USD ($) $ / MMBTU	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2018 Purchasers	Dec. 31, 2018	Dec. 31, 2018 $ / bbl	Dec. 31, 2018 $ / MMBTU	Dec. 31, 2018 shares
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Billing date	30 days
Outstanding days of account receivable	60 days
Allowance for doubtful accounts	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Number of purchasers | Purchasers			2						2						4
Capitalized general and administrative costs		30,000,000.0						31,100,000						$ 28,300,000
Capitalized interest expense		5,000,000.0						7,600,000						8,800,000
Depletion		334,800,000						330,700,000						251,800,000
Previous period used for price calculation	12 months
Present value discounted percent of future net revenues of proved oil and natural gas reserves				10.00%
Average oil and natural gas prices					36.04	1.99					52.19	2.58					62.04	3.10
Impairment charge of net capitalized costs		684,743,000						0						0
Stock-based compensation (non-cash) expense		13,625,000						18,505,000						17,200,000
Common stock and restricted stock unit expense		1,000,000.0						1,400,000						1,600,000
Compensation expense, liability-based awards		4,000,000.0						3,200,000
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable due period	30 days
Contract term after production	1 month
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable due period	60 days
Contract term after production	2 months
Sales Revenue, Goods, Net
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage				65.00%						67.00%						60.00%
Accounts Receivable
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage				35.00%						31.00%						34.00%
Plains Marketing, L.P. | Customer Concentration Risk | Sales Revenue, Goods, Net
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage				57.00%						53.00%						19.00%
BP America Production Company | Customer Concentration Risk | Sales Revenue, Goods, Net
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage										14.00%						15.00%
Exxon Mobil Corporate | Customer Concentration Risk | Sales Revenue, Goods, Net
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage				8.00%
Occidental Energy Marketing, Inc. | Customer Concentration Risk | Sales Revenue, Goods, Net
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage																14.00%
Western Refining Oil | Customer Concentration Risk | Sales Revenue, Goods, Net
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage																12.00%
Machinery and Equipment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Capitalized general and administrative costs		1,800,000						1,800,000						$ 1,600,000
Capitalized interest expense		$ 500,000						$ 900,000
Useful life using the straight-line	30 years
Machinery and Equipment | Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Useful life	5 years
Machinery and Equipment | Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Useful life	30 years
Employee Stock Options
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Antidilutive options excluded from calculation (in shares) | shares							2,500,000						2,600,000						1,600,000
Restricted Stock
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Antidilutive options excluded from calculation (in shares) | shares							700,000