Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued alternative fuels incentives	$ 34,068	$ 27,839
Accrued employee benefits	2,732	2,276
Accrued interest	285	220
Accrued gas and equipment purchases	9,170	11,383
Accrued property and other taxes	3,121	3,732
Accrued salaries and wages	4,439	9,105
Embedded derivatives	344	42
Other	12,372	13,100
Total accrued liabilities	$ 66,531	$ 67,697