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Statements of Changes in Partners' Capital (Parenthetical) - shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Statements of Changes in Partners' Capital      
Addition of partnership units 44,600,000 67,200,000 66,825,000
Redemption of partnership units 28,500,000 84,957,031 53,350,000