Other borrowings (Narrative) (Details) (USD $)
1 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Debt Disclosure [Abstract]        
Borrowing capacity as percent of total assets   20.00%    
FHLB borrowings outstanding Total   $ 0 $ 27,000,000  
FHLB, prepayments 60,000,000      
FHLB, weighted average interest rate 3.17%   0.25%  
Prepayment penalties   0 3,827,000 0
FHLB, maximum amount available   466,800,000    
FRB line of credit, amount outstanding   0    
Federal reserves bank, undrawn borrowing capcity   14,000,000    
Federal funds maximum borrowing capacity   90,000,000    
Federal funds outstanding borrowings   $ 0