Short-term borrowings (Parenthetical) (Details) - Pledged
Dec. 31, 2015
Dec. 31, 2014
Repurchase advance    
Assets Sold Under Agreements To Repurchase [Line Items]    
Federal Home Loan Bank interest rate 0.39%  
Cash management advance    
Assets Sold Under Agreements To Repurchase [Line Items]    
Federal Home Loan Bank interest rate 0.26% 0.45%