Contingent Liabilities, Commitments, and Financial Instruments with Off-Balance-Sheet Risk (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information
Off-balance-sheet instruments	$ 1,030,334	$ 868,267
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information
Off-balance-sheet instruments	29,961	33,397
Commercial and similar letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information
Off-balance-sheet instruments	$ 1,837	$ 1,704
Minimum | Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information
Letter of Credit Term	6 months
Minimum | Commercial and similar letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information
Letter of Credit Term	3 months
Maximum | Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information
Letter of Credit Term	1 year
Maximum | Commercial and similar letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information
Letter of Credit Term	6 months