Income taxes (Significant Components of the Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Reserve for loan losses and unfunded loan commitments	$ 10,431	$ 8,961
Deferred benefit plan expenses, net	13,663	12,768
Federal and state net operating loss and other carryforwards	14,840	28,068
Tax credit carryforwards	3,419	2,427
Allowance for losses on OREO	441	651
Accrued interest on non-accrual loans	125	169
Purchased intangibles	4,870	5,390
Fair value of acquired assets/liabilities	2,698	1,563
Other	1,464	575
Deferred tax assets	51,951	60,572
Valuation allowance for deferred tax assets	(59)	(74)
Deferred tax assets, net of valuation allowance	51,892	60,498
Deferred tax liabilities:
Accumulated depreciation and amortization	2,755	2,070
Deferred loan fees	1,240	1,233
FHLB stock dividends	289	2,242
Net unrealized gains (losses) on investment securities available-for-sale	(653)	994
Purchased intangibles	2,395	2,543
Other	694	743
Deferred tax liabilities	6,720	9,825
Net deferred tax assets (liabilities)	$ 45,172	$ 50,673