Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued alternative fuels incentives	$ 14,856	$ 27,839
Accrued employee benefits	3,357	2,276
Accrued interest	287	220
Accrued gas and equipment purchases	8,083	11,383
Accrued property and other taxes	3,625	3,732
Accrued salaries and wages	6,220	9,105
Embedded derivatives	715	42
Other	11,005	13,100
Total accrued liabilities	$ 48,148	$ 67,697