Annual report pursuant to Section 13 and 15(d)

CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical)

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CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
CONSOLIDATED STATEMENTS OF OPERATIONS      
Losses accrued on firm purchase commitments $ 0 $ 5,000,000 $ 0