Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details Textual)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2019 USD ($) $ / MMBTU	Dec. 31, 2019 USD ($) $ / bbl	Dec. 31, 2019 USD ($) Purchasers	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) shares	Dec. 31, 2018 USD ($) $ / MMBTU	Dec. 31, 2018 USD ($) $ / bbl	Dec. 31, 2018 USD ($) Purchasers	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 shares	Dec. 31, 2017 $ / MMBTU	Dec. 31, 2017 $ / bbl	Dec. 31, 2017 Purchasers	Dec. 31, 2017	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
RIght-of-use asset	$ 85,668,000	$ 85,668,000	$ 85,668,000	$ 85,668,000	$ 85,668,000	$ 85,668,000	$ 85,668,000													$ 62,300,000
Lease liability	$ 91,623,000	91,623,000	91,623,000	91,623,000	91,623,000	91,623,000	91,623,000													$ 62,300,000
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						4						4
Capitalized general and administrative costs							31,100,000						28,300,000						$ 23,100,000
Capitalized interest expense							7,600,000						8,800,000						7,300,000
Depletion							330,700,000						251,800,000						170,300,000
Present value discounted percent of future net revenues of proved oil and natural gas reserves						10.00%
Average oil and natural gas prices			2.58	52.19					3.10	62.04					2.98	47.79
Impairment charge of net capitalized costs							0						0						0
Stock-based compensation (non-cash) expense							18,505,000						17,200,000						16,654,000
Common stock and restricted stock unit expense							1,400,000						1,600,000						$ 3,000,000.0
Compensation expense, liability-based awards							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						67.00%						60.00%						60.00%
Accounts Receivable
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage						31.00%						34.00%						43.00%
Plains Marketing, L.P. | Customer Concentration Risk | Sales Revenue, Goods, Net
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage						53.00%						19.00%						14.00%
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%
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%												23.00%
Western Refining Oil | Customer Concentration Risk | Sales Revenue, Goods, Net
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration risk, percentage												12.00%						11.00%
Shell Trading (US) Company | 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						$ 1,600,000
Capitalized interest expense							$ 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		2,600,000						1,600,000						1,000,000.0