Commitments, guarantees and contingencies (Summary of the Bank's Off-balance Sheet Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet financial instruments	$ 550,431	$ 404,894
Commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet financial instruments	479,353	371,871
Commitments under credit card lines of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet financial instruments	65,988	28,822
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet financial instruments	$ 5,090	$ 4,201