Fair Value Measurements - Fair Value Recognition - Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income [Extensible List]	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax
Commodity swap contracts
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Beginning balance	$ 12,545	$ 5,362	$ 3,270	$ 10,332
Settlements, net	(453)	209	(477)	209
Total gain (loss)	(2,349)	125	6,950	(4,845)
Ending balance	9,743	5,696	9,743	5,696
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(2,802)	334	6,473	(4,636)
Embedded derivatives
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Beginning balance	143		723
Total gain (loss)	(49)	450	(629)	450
Ending balance	94	450	94	450
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ (49)	$ 450	$ (629)	$ 450