Fair Value - Change in Level 3 Financial Assets (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	$ 13,744	$ 170,181
Settlement of natural gas fixed price forward contracts	(3,605)	(3,412)
Embedded derivative on notes		6,291
Changes in fair value	3,005	19,529
Conversion of preferred stock warrants liability and derivative liability to common shares		(178,845)
Balance	13,144	13,744
Natural gas fixed price forward contract
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	9,729	15,368
Settlement of natural gas fixed price forward contracts	(3,605)	(3,412)
Embedded derivative on notes		0
Changes in fair value	844	(2,227)
Conversion of preferred stock warrants liability and derivative liability to common shares		0
Balance	6,968	9,729
Preferred stock warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	0	9,825
Settlement of natural gas fixed price forward contracts	0	0
Embedded derivative on notes		0
Changes in fair value	0	(8,943)
Conversion of preferred stock warrants liability and derivative liability to common shares		(882)
Balance	0	0
Embedded Derivative Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	0	140,771
Settlement of natural gas fixed price forward contracts	0	0
Embedded derivative on notes		6,288
Changes in fair value	0	30,904
Conversion of preferred stock warrants liability and derivative liability to common shares		(177,963)
Balance	0	0
Embedded EPP Derivative
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	4,015	4,217
Settlement of natural gas fixed price forward contracts	0	0
Embedded derivative on notes		3
Changes in fair value	2,161	(205)
Conversion of preferred stock warrants liability and derivative liability to common shares		0
Balance	$ 6,176	$ 4,015

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Conversion

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

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- Definition

Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of issuances of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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