Loans - Additional Information (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) loan	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net unamortized loan fees	$ 3,158,000		$ 3,175,000
Percentage of comprised loan, commercial, industrial and agricultural loans	38.00%		37.00%
Percentage of comprised loan, commercial mortgage loans	28.00%		28.00%
Percentage of loan-to-value to business equipment	80.00%
Percentage of loan-to-value to accounts receivable	75.00%
Percentage of loan-to-value to business inventory	60.00%
Percentage of loan-to-value to real estate	85.00%
Percentage of residential real estate loan in portfolio	31.00%		31.00%
Principal balances forgiven in connection with loan restructuring	$ 0	$ 0	$ 0
Minimum period to be considered for loan to have defaulted	90 days
Number of loans | loan	25		25
Modified in a troubled debt restructuring	$ 13,099,000		$ 14,626,000
Financing receivable, allowance for credit losses, w-downs	$ 818,000	$ 726,000
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum percentage of consumer loan and credit card in portfolio	4.00%		4.00%