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Stockholders' equity - Additional Information (Details) - $ / shares
3 Months Ended
Sep. 30, 2021
Jun. 30, 2021
Mar. 31, 2021
Sep. 30, 2020
Jun. 30, 2020
Mar. 31, 2020
Equity [Abstract]            
Cash dividends declared per common share (in dollars per share) $ 1.02 $ 1.02 $ 1.02 $ 0.90 $ 0.90 $ 0.90
Cash dividends paid per common share (in dollars per share) $ 1.02 $ 1.02 $ 1.02 $ 0.90 $ 0.90 $ 0.90