Income taxes (Significant Components of the Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets:
Reserve for loan losses and unfunded loan commitments	$ 8,961	$ 9,920
Deferred benefit plan expenses, net	12,768	11,942
Federal and state net operating loss and other carryforwards	28,068	39,532
Tax credit carryforwards	2,427	1,397
Allowance for losses on OREO	651	928
Accrued interest on non-accrual loans	169	2,240
Purchased intangibles	5,390	6,580
Fair value of acquired assets/liabilities	1,563	2,849
Other	575	793
Deferred tax assets	60,572	76,181
Valuation allowance for deferred tax assets	(74)	(78)	$ (100)	$ (41,700)
Deferred tax assets, net of valuation allowance	60,498	76,103
Deferred tax liabilities:
Accumulated depreciation and amortization	2,070	2,552
Deferred loan fees	1,233	(466)
FHLB stock dividends	2,242	2,289
Net unrealized gains on investment securities available-for-sale	994	1,765
Purchased intangibles	2,543	2,885
Other	743	952
Deferred tax liabilities	9,825	9,977
Net deferred tax assets (liabilities)	$ 50,673	$ 66,126