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Salaries and other employee expenses (Details 1) - Restricted Stocks [Member] - Directors [Member]
 12 Months Ended
Dec. 31, 2020
USD ($)
$ / shares
Dec. 31, 2019
USD ($)
$ / shares
Dec. 31, 2018
USD ($)
$ / shares
Disclosure Of Sharebased Payment Arrangements [Line Items]      
Number of Shares, Outstanding at Beginning 109,350 103,650 91,950
Number of Shares, Granted 63,000 57,000 57,000
Number of Shares, Vested (40,200) (51,300) (45,300)
Number of Shares, Outstanding at End 132,150 109,350 103,650
Number of Shares, Expected to vest 132,150    
Weighted average grand date fair value Outstanding at beginning | $ / shares $ 25.44 $ 27.82 $ 27.40
Weighted average grand date fair value, Granted | $ / shares 11.54 22.68 28.70
Weighted average grand date fair value, Vested | $ / shares 26.26 27.19 28.07
Weighted average grand date fair value, Outstanding at End | $ / shares $ 18.56 $ 25.44 $ 27.82