Loans - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) payment	Dec. 31, 2017 USD ($) payment	Dec. 31, 2016 USD ($) payment
Receivables [Abstract]
Reduction in interest income	$ 1,000,000	$ 700,000	$ 700,000
Loans to directors and executive officers	900,000	1,100,000
New loans offered	0
Loans pledged as collateral for borrowings	$ 380,000,000	$ 211,000,000
Payments for loans in default, number of payments | payment	0	0	0
Accruals for trouble debt restructurings	$ 13,300,000	$ 15,600,000
Average amount for loans impaired	35,300,000	30,900,000	$ 31,200,000
Interest income on impaired loans	2,000,000	1,500,000	1,600,000
Interest income related to impaired loans with impairment measured on present value of expected future cash flows	$ 200,000	$ 300,000	$ 200,000