Annual report pursuant to Section 13 and 15(d)

CONSOLIDATED STATEMENTS OF INCOME (Parenthetical)

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CONSOLIDATED STATEMENTS OF INCOME (Parenthetical) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
OPERATING COSTS AND EXPENSES      
Depreciation and amortization included in the cost of petrochemical, product sales, and processing $ 10,089 $ 9,016 $ 8,335