Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2016
Accounting Policies [Abstract]  
Activity regarding the allowance for doubtful accounts
Activity regarding the allowance for doubtful accounts was as follows:
Balance, January 1, 2014
$
2,124

Amount charged to selling, general and administrative expenses
1,453

Charge-offs, net of recoveries
(1,304
)
Balance, December 31, 2014
2,273

Amount charged to selling, general and administrative expenses
(803
)
Charge-offs, net of recoveries
(119
)
Balance, December 31, 2015
1,351

Amount charged to selling, general and administrative expenses
630

Charge-offs, net of recoveries
(106
)
Balance, December 31, 2016
$
1,875
Estimated useful lives
Depreciation expense is computed on a straight-line method based upon estimated useful lives of the assets. Estimated useful lives are as follows:
 
Automobiles and trucks
5 years
Computers and office equipment
5 years
Office furniture and fixtures
7 years
Machinery and equipment
5-30 years
Leasehold improvements
the lesser of the lease term or 30 years
Buildings and improvements
30-40 years
Concentration risk by customer
One customer represented slightly less than 10% of the total consolidated revenues of the Company for the years ended December 31, 2016 and 2015. This customer accounted for more than 10% of the total consolidated revenues of the Company for the year ended December 31, 2014. All customer amounts disclosed in the table are related to biomass-based diesel sales:
 
2016
 
2015
 
2014
Customer A
$
144,849

 
$
114,030

 
$
231,780