Income taxes (Significant Components of the Net Deferred Tax Assets and Liabilities (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Deferred tax assets:      
Reserve for loan losses and unfunded loan commitments $ 9,920 $ 8,530  
Deferred benefit plan expenses, net 11,942 8,700  
Federal and state net operating loss and other carryforwards 39,532 33,823  
Tax credit carryforwards 1,397 1,112  
Allowance for losses on OREO 928 2,167  
Accrued interest on non-accrual loans 2,240 231  
Purchased intangibles 6,580 86  
Fair value of acquired assets/liabilities 2,849 0  
Net unrealized loss on investment securities available-for-sale 0 21  
Other 793 284  
Deferred tax assets 76,181 54,954  
Valuation allowance for deferred tax assets (78) (74) (41,700)
Deferred tax assets, net of valuation allowance 76,103 54,880  
Deferred tax liabilities:      
Accumulated depreciation and amortization 2,552 2,821  
Deferred loan fees (466) 711  
FHLB stock dividends 2,289 556  
Net unrealized gains on investment securities available-for-sale 1,765 0  
Purchased intangibles 2,885 0  
Other 952 724  
Deferred tax liabilities 9,977 4,812  
Net deferred tax assets (liabilities) $ 66,126 $ 50,068