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Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2017
Accounting Policies [Abstract]  
Property Plant And Equipment Estimated Useful Life
We compute depreciation of property, plant, and equipment using the straight-line method, based on the estimated useful life of each asset as follows:
Assets
 
Lives in Years
Refining
 
8 to 47
Logistics
 
3 to 30
Retail
 
14 to 18
Corporate
 
3 to 7
Software
 
3
Summary of Depreciation Expense
The following table summarizes depreciation expense excluded from each line item in our consolidated statements of operations (in thousands):
 
 
Year Ended December 31,
 
 
2017
 
2016
 
2015
Cost of revenues
 
$
6,029

 
$
4,604

 
$
3,017

Operating expense
 
22,861

 
16,340

 
11,428

General and administrative expense
 
2,929

 
2,108

 
855