Commitments and Financial Instruments with Off-Balance-Sheet Risk (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Loan commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance-sheet instruments	$ 1,031,638	$ 1,030,334
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance-sheet instruments	$ 31,421	29,961
Standby letters of credit | Minimum
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Letter of credit term	6 months
Standby letters of credit | Maximum
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Letter of credit term	1 year
Commercial and similar letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance-sheet instruments	$ 756	$ 1,837
Commercial and similar letters of credit | Minimum
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Letter of credit term	3 months
Commercial and similar letters of credit | Maximum
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Letter of credit term	6 months