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Derivatives - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	2 Months Ended	10 Months Ended	12 Months Ended
Derivatives - Narrative (Details) - USD ($) $ in Thousands	May 31, 2018	Feb. 28, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Target period to cover operating expenses and fixed charges (up to)				2 years
Target period for fixing the price natural gas purchases used in steam operations (up to)				2 years
Purchased put options premium				$ 17,000
Deferred premiums, remaining				55
Derivative termination costs	$ 127,000
Cash settlements received on derivatives		$ 3,000	$ 500	42,000
Cash settlements paid on normal derivatives		$ (534)	$ (3,068)	$ (42,197)	$ 38,482