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Summary of significant accounting policies (Details) - USD ($)
$ in Thousands
 6 Months Ended
Jun. 30, 2020
Jan. 01, 2020
Dec. 31, 2019
Summary Of Significant Accounting Policies [Line Items]      
Allowance for credit loss $ 64,263   $ 0
Decrease to retained earnings $ (8,232,470)   (7,734,609)
Accounting Standards Update [Extensible List] us-gaap:AccountingStandardsUpdate201613Member    
Cumulative effect due to adoption of new accounting standard      
Summary Of Significant Accounting Policies [Line Items]      
Allowance for credit loss   $ 30,300 $ 30,264
Decrease to retained earnings   $ 25,800