Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 02, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued alternative fuels incentives	$ 27,839		$ 6,923
Accrued employee benefits	2,276		2,248
Accrued interest	220		78
Accrued gas and equipment purchases	11,383		12,833
Accrued property and other taxes	3,732		3,397
Salaries and wages	9,105		8,609
Other	13,142		14,381
Total accrued liabilities	$ 67,697	$ 47,973	$ 48,469