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Financial instruments (Details 17) - Series H bonds [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Principal payment [Member]      
Financial instruments [Line Items]      
Repayments of bonds, notes and debentures $ 6,601 $ 7,868 $ 8,325
CCS Coverage [Member]      
Financial instruments [Line Items]      
Repayments of bonds, notes and debentures $ 2,575 $ 1,952 $ 495